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Novak JK, Gardner JG. Current models in bacterial hemicellulase-encoding gene regulation. Appl Microbiol Biotechnol 2024; 108:39. [PMID: 38175245 PMCID: PMC10766802 DOI: 10.1007/s00253-023-12977-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 12/06/2023] [Accepted: 12/07/2023] [Indexed: 01/05/2024]
Abstract
The discovery and characterization of bacterial carbohydrate-active enzymes is a fundamental component of biotechnology innovation, particularly for renewable fuels and chemicals; however, these studies have increasingly transitioned to exploring the complex regulation required for recalcitrant polysaccharide utilization. This pivot is largely due to the current need to engineer and optimize enzymes for maximal degradation in industrial or biomedical applications. Given the structural simplicity of a single cellulose polymer, and the relatively few enzyme classes required for complete bioconversion, the regulation of cellulases in bacteria has been thoroughly discussed in the literature. However, the diversity of hemicelluloses found in plant biomass and the multitude of carbohydrate-active enzymes required for their deconstruction has resulted in a less comprehensive understanding of bacterial hemicellulase-encoding gene regulation. Here we review the mechanisms of this process and common themes found in the transcriptomic response during plant biomass utilization. By comparing regulatory systems from both Gram-negative and Gram-positive bacteria, as well as drawing parallels to cellulase regulation, our goals are to highlight the shared and distinct features of bacterial hemicellulase-encoding gene regulation and provide a set of guiding questions to improve our understanding of bacterial lignocellulose utilization. KEY POINTS: • Canonical regulatory mechanisms for bacterial hemicellulase-encoding gene expression include hybrid two-component systems (HTCS), extracytoplasmic function (ECF)-σ/anti-σ systems, and carbon catabolite repression (CCR). • Current transcriptomic approaches are increasingly being used to identify hemicellulase-encoding gene regulatory patterns coupled with computational predictions for transcriptional regulators. • Future work should emphasize genetic approaches to improve systems biology tools available for model bacterial systems and emerging microbes with biotechnology potential. Specifically, optimization of Gram-positive systems will require integration of degradative and fermentative capabilities, while optimization of Gram-negative systems will require bolstering the potency of lignocellulolytic capabilities.
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Affiliation(s)
- Jessica K Novak
- Department of Biological Sciences, University of Maryland - Baltimore County, Baltimore, MD, USA
| | - Jeffrey G Gardner
- Department of Biological Sciences, University of Maryland - Baltimore County, Baltimore, MD, USA.
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2
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Daley SR, Kirby S, Sparling R. Adaptive evolution of Clostridium thermocellum ATCC 27405 on alternate carbon sources leads to altered fermentation profiles. Can J Microbiol 2024. [PMID: 38832648 DOI: 10.1139/cjm-2024-0004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/05/2024]
Abstract
Consolidated bioprocessing candidate, Clostridium thermocellum, is a cellulose hydrolysis specialist, with the ability to ferment the released sugars to produce bioethanol. C. thermocellum is generally studied with model substrates Avicel and cellobiose to understand the metabolic pathway leading to ethanol. In the present study, adaptive laboratory evolution, allowing C. thermocellum DSM 1237 to adapt to growth on glucose, fructose, and sorbitol, with the prospect that some strains will adapt their metabolism to yield more ethanol. Adaptive growth on glucose and sorbitol resulted in an approximately 1 mM and 2 mM increase in ethanol yield per millimolar glucose equivalent, respectively, accompanied by a shift in the production of the other expected fermentation end products. The increase in ethanol yield observed for sorbitol adapted cells was due to the carbon source being more reduced compared to cellobiose. Glucose and cellobiose have similar oxidation states thus the increase in ethanol yield is due to the rerouting of electrons from other reduced metabolic products excluding H2 which did not decrease in yield. There was no increase in ethanol yield observed for fructose adapted cells, but there was an unanticipated elimination of formate production, also observed in sorbitol adapted cells suggesting that fructose has regulatory implications on formate production either at the transcription or protein level.
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Affiliation(s)
- Steve R Daley
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada
| | - Samantha Kirby
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada
| | - Richard Sparling
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada
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3
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Callaghan MM, Thusoo E, Sharma BD, Getahun F, Stevenson DM, Maranas C, Olson DG, Lynd LR, Amador-Noguez D. Deuterated water as a substrate-agnostic isotope tracer for investigating reversibility and thermodynamics of reactions in central carbon metabolism. Metab Eng 2023; 80:254-266. [PMID: 37923005 DOI: 10.1016/j.ymben.2023.10.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 10/16/2023] [Accepted: 10/22/2023] [Indexed: 11/07/2023]
Abstract
Stable isotope tracers are a powerful tool for the quantitative analysis of microbial metabolism, enabling pathway elucidation, metabolic flux quantification, and assessment of reaction and pathway thermodynamics. 13C and 2H metabolic flux analysis commonly relies on isotopically labeled carbon substrates, such as glucose. However, the use of 2H-labeled nutrient substrates faces limitations due to their high cost and limited availability in comparison to 13C-tracers. Furthermore, isotope tracer studies in industrially relevant bacteria that metabolize complex substrates such as cellulose, hemicellulose, or lignocellulosic biomass, are challenging given the difficulty in obtaining these as isotopically labeled substrates. In this study, we examine the potential of deuterated water (2H2O) as an affordable, substrate-neutral isotope tracer for studying central carbon metabolism. We apply 2H2O labeling to investigate the reversibility of glycolytic reactions across three industrially relevant bacterial species -C. thermocellum, Z. mobilis, and E. coli-harboring distinct glycolytic pathways with unique thermodynamics. We demonstrate that 2H2O labeling recapitulates previous reversibility and thermodynamic findings obtained with established 13C and 2H labeled nutrient substrates. Furthermore, we exemplify the utility of this 2H2O labeling approach by applying it to high-substrate C. thermocellum fermentations -a setting in which the use of conventional tracers is impractical-thereby identifying the glycolytic enzyme phosphofructokinase as a major bottleneck during high-substrate fermentations and unveiling critical insights that will steer future engineering efforts to enhance ethanol production in this cellulolytic organism. This study demonstrates the utility of deuterated water as a substrate-agnostic isotope tracer for examining flux and reversibility of central carbon metabolic reactions, which yields biological insights comparable to those obtained using costly 2H-labeled nutrient substrates.
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Affiliation(s)
- Melanie M Callaghan
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA
| | - Eashant Thusoo
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA; Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
| | - Bishal D Sharma
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Fitsum Getahun
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA; Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
| | - David M Stevenson
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA; Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA
| | - Costas Maranas
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, USA
| | - Daniel G Olson
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Lee R Lynd
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
| | - Daniel Amador-Noguez
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, USA; Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, USA; Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, Madison, WI, USA.
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Daley SR, Gallanosa PM, Sparling R. Kinetic characterization of annotated glycolytic enzymes present in cellulose-fermenting Clostridium thermocellum suggests different metabolic roles. BIOTECHNOLOGY FOR BIOFUELS AND BIOPRODUCTS 2023; 16:112. [PMID: 37438781 DOI: 10.1186/s13068-023-02362-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Accepted: 06/27/2023] [Indexed: 07/14/2023]
Abstract
BACKGROUND The efficient production of sustainable biofuels is important for the reduction of greenhouse gas emissions. Clostridium thermocellum ATCC 27405 is a candidate for ethanol production from lignocellulosic biomass using consolidated bioprocessing. Fermentation of cellulosic biomass goes through an atypical glycolytic pathway in this thermophilic bacterium, with various glycolytic enzymes capable of utilizing different phosphate donors, including GTP and inorganic pyrophosphate (PPi), in addition to or in place of the usual ATP. C. thermocellum contains three annotated phosphofructokinases (PFK) genes, the expression of which have all been detected through proteomics and transcriptomics. Pfp (Cthe_0347) was previously characterized as pyrophosphate dependent with fructose-6-phosphate (F6P) as its substrate. RESULTS We now demonstrate that this enzyme can also phosphorylate sedoheptulose-7-phosphate (an intermediate in the pentose phosphate pathway), with the Vmax and Km of F6P being approximately 15 folds higher and 43 folds lower, respectively, in comparison to sedoheptulose-7-phosphate. Purified PfkA shows preference for GTP as the phosphate donor as opposed to ATP with a 12.5-fold difference in Km values while phosphorylating F6P. Allosteric regulation is a factor at play in PfkA activity, with F6P exhibiting positive cooperativity, and an apparent requirement for ammonium ions to attain maximal activity. Phosphoenolpyruvate and PPi were the only inhibitors for PfkA determined from the study, which corroborates what is known about enzymes from this subfamily. The activation or inhibition by these ligands lends support to the argument that glycolysis is regulated by metabolites such as PPi and NH4+ in the organism. PfkB, showed no activity with F6P, but had significant activity with fructose, while utilizing either ATP or GTP, making it a fructokinase. Rounding out the upper glycolysis pathway, the identity of the fructose-1,6-bisphosphate aldolase in the genome was verified and reported to have substantial activity with fructose-1,6-bisphosphate, in the presence of the divalent ion, Zn2+. CONCLUSION These findings along with previous proteomic data suggest that Pfp, plays a role in both glycolysis and the pentose phosphate pathway, while PfkA and PfkB may phosphorylate sugars in glycolysis but is responsible for sugar metabolism elsewhere under conditions outside of growth on sufficient cellobiose.
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Affiliation(s)
- Steve R Daley
- Department of Microbiology, University of Manitoba, 213 Buller Building, Winnipeg, MB, R3T 2N2, Canada
| | - Patricia Mae Gallanosa
- Department of Microbiology, University of Manitoba, 213 Buller Building, Winnipeg, MB, R3T 2N2, Canada
| | - Richard Sparling
- Department of Microbiology, University of Manitoba, 213 Buller Building, Winnipeg, MB, R3T 2N2, Canada.
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Kuil T, Nurminen CMK, van Maris AJA. Pyrophosphate as allosteric regulator of ATP-phosphofructokinase in Clostridium thermocellum and other bacteria with ATP- and PP i-phosphofructokinases. Arch Biochem Biophys 2023; 743:109676. [PMID: 37380119 DOI: 10.1016/j.abb.2023.109676] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2023] [Revised: 06/13/2023] [Accepted: 06/17/2023] [Indexed: 06/30/2023]
Abstract
The phosphofructokinase (Pfk) reaction represents one of the key regulatory points in glycolysis. While most organisms encode for Pfks that use ATP as phosphoryl donor, some organisms also encode for PPi-dependent Pfks. Despite this central role, the biochemical characteristics as well as the physiological role of both Pfks is often not known. Clostridium thermocellum is an example of a microorganism that encodes for both Pfks, however, only PPi-Pfk activity has been detected in cell-free extracts and little is known about the regulation and function of both enzymes. In this study, the ATP- and PPi-Pfk of C. thermocellum were purified and biochemically characterized. No allosteric regulators were found for PPi-Pfk amongst common effectors. With fructose-6-P, PPi, fructose-1,6-bisP, and Pi PPi-Pfk showed high specificity (KM < 0.62 mM) and maximum activity (Vmax > 156 U mg-1). In contrast, ATP-Pfk showed much lower affinity (K0.5 of 9.26 mM) and maximum activity (14.5 U mg-1) with fructose-6-P. In addition to ATP, also GTP, UTP and ITP could be used as phosphoryl donors. The catalytic efficiency with GTP was 7-fold higher than with ATP, suggesting that GTP is the preferred substrate. The enzyme was activated by NH4+, and pronounced inhibition was observed with GDP, FBP, PEP, and especially with PPi (Ki of 0.007 mM). Characterization of purified ATP-Pfks originating from eleven different bacteria, encoding for only ATP-Pfk or for both ATP- and PPi-Pfk, identified that PPi inhibition of ATP-Pfks could be a common phenomenon for organisms with a PPi-dependent glycolysis.
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Affiliation(s)
- Teun Kuil
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Carolus M K Nurminen
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Antonius J A van Maris
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden.
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The Roles of Nicotinamide Adenine Dinucleotide Phosphate Reoxidation and Ammonium Assimilation in the Secretion of Amino Acids as Byproducts of Clostridium thermocellum. Appl Environ Microbiol 2023; 89:e0175322. [PMID: 36625594 PMCID: PMC9888227 DOI: 10.1128/aem.01753-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
Clostridium thermocellum is a cellulolytic thermophile that is considered for the consolidated bioprocessing of lignocellulose to ethanol. Improvements in ethanol yield are required for industrial implementation, but the incompletely understood causes of amino acid secretion impede progress. In this study, amino acid secretion was investigated via gene deletions in ammonium-regulated, nicotinamide adenine dinucleotide phosphate (NADPH)-supplying and NADPH-consuming pathways as well as via physiological characterization in cellobiose-limited or ammonium-limited chemostats. First, the contribution of the NADPH-supplying malate shunt was studied with strains using either the NADPH-yielding malate shunt (Δppdk) or a redox-independent conversion of PEP to pyruvate (Δppdk ΔmalE::Peno-pyk). In the latter, branched-chain amino acids, especially valine, were significantly reduced, whereas the ethanol yield increased from 46 to 60%, suggesting that the secretion of these amino acids balances the NADPH surplus from the malate shunt. The unchanged amino acid secretion in Δppdk falsified a previous hypothesis on an ammonium-regulated PEP-to-pyruvate flux redistribution. The possible involvement of another NADPH-supplier, namely, NADH-dependent reduced ferredoxin:NADP+ oxidoreductase (nfnAB), was also excluded. Finally, the deletion of glutamate synthase (gogat) in ammonium assimilation resulted in the upregulation of NADPH-linked glutamate dehydrogenase activity and decreased amino acid yields. Since gogat in C. thermocellum is putatively annotated as ferredoxin-linked, a claim which is supported by the product redistribution observed in this study, this deletion likely replaced ferredoxin with NADPH in ammonium assimilation. Overall, these findings indicate that a need to reoxidize NADPH is driving the observed amino acid secretion, likely at the expense of the NADH needed for ethanol formation. This suggests that metabolic engineering strategies that simplify the redox metabolism and ammonium assimilation can contribute to increased ethanol yields. IMPORTANCE Improving the ethanol yield of C. thermocellum is important for the industrial implementation of this microorganism in consolidated bioprocessing. A central role of NADPH in driving amino acid byproduct formation was demonstrated by eliminating the NADPH-supplying malate shunt and separately by changing the cofactor specificity in ammonium assimilation. With amino acid secretion diverting carbon and electrons away from ethanol, these insights are important for further metabolic engineering to reach industrial requirements on ethanol yield. This study also provides chemostat data that are relevant for training genome-scale metabolic models and for improving the validity of their predictions, especially considering the reduced degree-of-freedom in the redox metabolism of the strains generated here. In addition, this study advances the fundamental understanding on the mechanisms underlying amino acid secretion in cellulolytic Clostridia as well as on the regulation and cofactor specificity in ammonium assimilation. Together, these efforts aid in the development of C. thermocellum for the sustainable consolidated bioprocessing of lignocellulose to ethanol with minimal pretreatment.
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Kuil T, Yayo J, Pechan J, Küchler J, van Maris AJA. Ethanol tolerance of Clostridium thermocellum: the role of chaotropicity, temperature and pathway thermodynamics on growth and fermentative capacity. Microb Cell Fact 2022; 21:273. [PMID: 36567317 PMCID: PMC9790125 DOI: 10.1186/s12934-022-01999-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2022] [Accepted: 12/17/2022] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Clostridium thermocellum is a promising candidate for consolidated bioprocessing of lignocellulosic biomass to ethanol. The low ethanol tolerance of this microorganism is one of the remaining obstacles to industrial implementation. Ethanol inhibition can be caused by end-product inhibition and/or chaotropic-induced stress resulting in increased membrane fluidization and disruption of macromolecules. The highly reversible glycolysis of C. thermocellum might be especially sensitive to end-product inhibition. The chaotropic effect of ethanol is known to increase with temperature. This study explores the relative contributions of these two aspects to investigate and possibly mitigate ethanol-induced stress in growing and non-growing C. thermocellum cultures. RESULTS To separate chaotropic from thermodynamic effects of ethanol toxicity, a non-ethanol producing strain AVM062 (Pclo1313_2638::ldh* ∆adhE) was constructed by deleting the bifunctional acetaldehyde/alcohol dehydrogenase gene, adhE, in a lactate-overproducing strain. Exogenously added ethanol lowered the growth rate of both wild-type and the non-ethanol producing mutant. The mutant strain grew quicker than the wild-type at 50 and 55 °C for ethanol concentrations ≥ 10 g L-1 and was able to reach higher maximum OD600 at all ethanol concentrations and temperatures. For the wild-type, the maximum OD600 and relative growth rates were higher at 45 and 50 °C, compared to 55 °C, for ethanol concentrations ≥ 15 g L-1. For the mutant strain, no positive effect on growth was observed at lower temperatures. Growth-arrested cells of the wild-type demonstrated improved fermentative capacity over time in the presence of ethanol concentrations up to 40 g L-1 at 45 and 50 °C compared to 55 °C. CONCLUSION Positive effects of temperature on ethanol tolerance were limited to wild-type C. thermocellum and are likely related to mechanisms involved in the ethanol-formation pathway and redox cofactor balancing. Lowering the cultivation temperature provides an attractive strategy to improve growth and fermentative capacity at high ethanol titres in high-cellulose loading batch cultivations. Finally, non-ethanol producing strains are useful platform strains to study the effects of chaotropicity and thermodynamics related to ethanol toxicity and allow for deeper understanding of growth and/or fermentation cessation under industrially relevant conditions.
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Affiliation(s)
- Teun Kuil
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Johannes Yayo
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Johanna Pechan
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Jan Küchler
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden ,grid.5807.a0000 0001 1018 4307Present Address: Max Plank Institute for Dynamics of Complex Technical Systems, Otto-Von-Guericke-University Magdeburg, Magdeburg, Germany
| | - Antonius J. A. van Maris
- grid.5037.10000000121581746Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
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Increasing the Thermodynamic Driving Force of the Phosphofructokinase Reaction in
Clostridium thermocellum. Appl Environ Microbiol 2022; 88:e0125822. [PMID: 36286488 PMCID: PMC9680637 DOI: 10.1128/aem.01258-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The ability to control the distribution of thermodynamic driving force throughout a metabolic pathway is likely to be an important tool for metabolic engineering. The phosphofructokinase reaction is a key enzyme in Embden-Mayerhof-Parnas glycolysis and therefore improving the thermodynamic driving force of this reaction in
C. thermocellum
is believed to enable higher product titers.
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Deciphering Cellodextrin and Glucose Uptake in Clostridium thermocellum. mBio 2022; 13:e0147622. [PMID: 36069444 PMCID: PMC9601137 DOI: 10.1128/mbio.01476-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
Sugar uptake is of great significance in industrially relevant microorganisms. Clostridium thermocellum has extensive potential in lignocellulose biorefineries as an environmentally prominent, thermophilic, cellulolytic bacterium. The bacterium employs five putative ATP-binding cassette transporters which purportedly take up cellulose hydrolysates. Here, we first applied combined genetic manipulations and biophysical titration experiments to decipher the key glucose and cellodextrin transporters. In vivo gene inactivation of each transporter and in vitro calorimetric and nuclear magnetic resonance (NMR) titration of each putative sugar-binding protein with various saccharides supported the conclusion that only transporters A and B play the roles of glucose and cellodextrin transport, respectively. To gain insight into the structural mechanism of the transporter specificities, 11 crystal structures, both alone and in complex with appropriate saccharides, were solved for all 5 putative sugar-binding proteins, thus providing detailed specific interactions between the proteins and the corresponding saccharides. Considering the importance of transporter B as the major cellodextrin transporter, we further identified its cryptic, hitherto unknown ATPase-encoding gene as clo1313_2554, which is located outside the transporter B gene cluster. The crystal structure of the ATPase was solved, showing that it represents a typical nucleotide-binding domain of the ATP-binding cassette (ABC) transporter. Moreover, we determined that the inducing effect of cellobiose (G2) and cellulose on cellulosome production could be eliminated by deletion of transporter B genes, suggesting the coupling of sugar transport and regulation of cellulosome components. This study provides key basic information on the sugar uptake mechanism of C. thermocellum and will promote rational engineering of the bacterium for industrial application.
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Bhalla A, Arce J, Ubanwa B, Singh G, Sani RK, Balan V. Thermophilic Geobacillus WSUCF1 Secretome for Saccharification of Ammonia Fiber Expansion and Extractive Ammonia Pretreated Corn Stover. Front Microbiol 2022; 13:844287. [PMID: 35694290 PMCID: PMC9176393 DOI: 10.3389/fmicb.2022.844287] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Accepted: 03/18/2022] [Indexed: 11/13/2022] Open
Abstract
A thermophilic Geobacillus bacterial strain, WSUCF1 contains different carbohydrate-active enzymes (CAZymes) capable of hydrolyzing hemicellulose in lignocellulosic biomass. We used proteomic, genomic, and bioinformatic tools, and genomic data to analyze the relative abundance of cellulolytic, hemicellulolytic, and lignin modifying enzymes present in the secretomes. Results showed that CAZyme profiles of secretomes varied based on the substrate type and complexity, composition, and pretreatment conditions. The enzyme activity of secretomes also changed depending on the substrate used. The secretomes were used in combination with commercial and purified enzymes to carry out saccharification of ammonia fiber expansion (AFEX)-pretreated corn stover and extractive ammonia (EA)-pretreated corn stover. When WSUCF1 bacterial secretome produced at different conditions was combined with a small percentage of commercial enzymes, we observed efficient saccharification of EA-CS, and the results were comparable to using a commercial enzyme cocktail (87% glucan and 70% xylan conversion). It also opens the possibility of producing CAZymes in a biorefinery using inexpensive substrates, such as AFEX-pretreated corn stover and Avicel, and eliminates expensive enzyme processing steps that are used in enzyme manufacturing. Implementing in-house enzyme production is expected to significantly reduce the cost of enzymes and biofuel processing cost.
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Affiliation(s)
- Aditya Bhalla
- Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, United States
- Department of Chemistry, Biology and Health Science, South Dakota School of Mines and Technology, Rapid City, SD, United States
- Great Lakes Bioenergy Center, Michigan State University, East Lansing, MI, United States
| | - Jessie Arce
- Department of Engineering Technology, College of Technology, University of Houston, Houston, TX, United States
| | - Bryan Ubanwa
- Department of Engineering Technology, College of Technology, University of Houston, Houston, TX, United States
| | - Gursharan Singh
- Department of Medical Laboratory Sciences, Lovely Professional University, Phagwara, India
| | - Rajesh K. Sani
- Department of Chemical and Biological Engineering, South Dakota School of Mines and Technology, Rapid City, SD, United States
- Department of Chemistry, Biology and Health Science, South Dakota School of Mines and Technology, Rapid City, SD, United States
| | - Venkatesh Balan
- Great Lakes Bioenergy Center, Michigan State University, East Lansing, MI, United States
- Department of Engineering Technology, College of Technology, University of Houston, Houston, TX, United States
- *Correspondence: Venkatesh Balan,
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11
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Functional analysis of H +-pumping membrane-bound pyrophosphatase, ADP-glucose synthase, and pyruvate phosphate dikinase as pyrophosphate sources in Clostridium thermocellum. Appl Environ Microbiol 2021; 88:e0185721. [PMID: 34936842 PMCID: PMC8863071 DOI: 10.1128/aem.01857-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The atypical glycolysis of Clostridium thermocellum is characterized by the use of pyrophosphate (PPi) as phosphoryl donor for phosphofructokinase (Pfk) and pyruvate phosphate dikinase (Ppdk) reactions. Previously, biosynthetic PPi was calculated to be stoichiometrically insufficient to drive glycolysis. This study investigates the role of a H+-pumping membrane-bound pyrophosphatase, glycogen cycling, a predicted Ppdk-malate shunt cycle and acetate cycling in generating PPi. Knockout studies and enzyme assays confirmed that clo1313_0823 encodes a membrane-bound pyrophosphatase. Additionally, clo1313_0717-0718 was confirmed to encode ADP-glucose synthase by knockouts, glycogen measurements in C. thermocellum and heterologous expression in E. coli. Unexpectedly, individually-targeted gene deletions of the four putative PPi sources did not have a significant phenotypic effect. Although combinatorial deletion of all four putative PPi sources reduced the growth rate by 22% (0.30±0.01 h-1) and the biomass yield by 38% (0.18±0.00 gbiomass gsubstrate-1), this change was much smaller than what would be expected for stoichiometrically essential PPi-supplying mechanisms. Growth-arrested cells of the quadruple knockout readily fermented cellobiose indicating that the unknown PPi-supplying mechanisms are independent of biosynthesis. An alternative hypothesis that ATP-dependent Pfk activity circumvents a need for PPi altogether, was falsified by enzyme assays, heterologous expression of candidate genes and whole-genome sequencing. As a secondary outcome, enzymatic assays confirmed functional annotation of clo1313_1832 as ATP- and GTP-dependent fructokinase. These results indicate that the four investigated PPi sources individually and combined play no significant PPi-supplying role and the true source(s) of PPi, or alternative phosphorylating mechanisms, that drive glycolysis in C. thermocellum remain(s) elusive. IMPORTANCE Increased understanding of the central metabolism of C. thermocellum is important from a fundamental as well as from a sustainability and industrial perspective. In addition to showing that H+-pumping membrane-bound PPase, glycogen cycling, a Ppdk-malate shunt cycle, and acetate cycling are not significant sources of PPi supply, this study adds functional annotation of four genes and availability of an updated PPi stoichiometry from biosynthesis to the scientific domain. Together, this aids future metabolic engineering attempts aimed to improve C. thermocellum as a cell factory for sustainable and efficient production of ethanol from lignocellulosic material through consolidated bioprocessing with minimal pretreatment. Getting closer to elucidating the elusive source of PPi, or alternative phosphorylating mechanisms, for the atypical glycolysis is itself of fundamental importance. Additionally, the findings of this study directly contribute to investigations into trade-offs between thermodynamic driving force versus energy yield of PPi- and ATP-dependent glycolysis.
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Utilization of Monosaccharides by Hungateiclostridium thermocellum ATCC 27405 through Adaptive Evolution. Microorganisms 2021; 9:microorganisms9071445. [PMID: 34361881 PMCID: PMC8303734 DOI: 10.3390/microorganisms9071445] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2021] [Revised: 06/30/2021] [Accepted: 07/02/2021] [Indexed: 12/13/2022] Open
Abstract
Hungateiclostridium thermocellum ATCC 27405 is a promising bacterium for consolidated bioprocessing with a robust ability to degrade lignocellulosic biomass through a multienzyme cellulosomal complex. The bacterium uses the released cellodextrins, glucose polymers of different lengths, as its primary carbon source and energy. In contrast, the bacterium exhibits poor growth on monosaccharides such as fructose and glucose. This phenomenon raises many important questions concerning its glycolytic pathways and sugar transport systems. Until now, the detailed mechanisms of H. thermocellum adaptation to growth on hexose sugars have been relatively poorly explored. In this study, adaptive laboratory evolution was applied to train the bacterium in hexose sugars-based media, and genome resequencing was used to detect the genes that got mutated during adaptation period. RNA-seq data of the first culture growing on either fructose or glucose revealed that several glycolytic genes in the Embden–Mayerhof–Parnas pathway were expressed at lower levels in these cells than in cellobiose-grown cells. After seven consecutive transfer events on fructose and glucose (~42 generations for fructose-adapted cells and ~40 generations for glucose-adapted cells), several genes in the EMP glycolysis of the evolved strains increased the levels of mRNA expression, accompanied by a faster growth, a greater biomass yield, a higher ethanol titer than those in their parent strains. Genomic screening also revealed several mutation events in the genomes of the evolved strains, especially in those responsible for sugar transport and central carbon metabolism. Consequently, these genes could be applied as potential targets for further metabolic engineering to improve this bacterium for bio-industrial usage.
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Yayo J, Kuil T, Olson DG, Lynd LR, Holwerda EK, van Maris AJA. Laboratory Evolution and Reverse Engineering of Clostridium thermocellum for Growth on Glucose and Fructose. Appl Environ Microbiol 2021; 87:e03017-20. [PMID: 33608285 PMCID: PMC8091016 DOI: 10.1128/aem.03017-20] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2020] [Accepted: 02/10/2021] [Indexed: 02/04/2023] Open
Abstract
The native ability of Clostridium thermocellum to efficiently solubilize cellulose makes it an interesting platform for sustainable biofuel production through consolidated bioprocessing. Together with other improvements, industrial implementation of C. thermocellum, as well as fundamental studies into its metabolism, would benefit from improved and reproducible consumption of hexose sugars. To investigate growth of C. thermocellum on glucose or fructose, as well as the underlying molecular mechanisms, laboratory evolution was performed in carbon-limited chemostats with increasing concentrations of glucose or fructose and decreasing cellobiose concentrations. Growth on both glucose and fructose was achieved with biomass yields of 0.09 ± 0.00 and 0.18 ± 0.00 gbiomass gsubstrate-1, respectively, compared to 0.15 ± 0.01 gbiomass gsubstrate-1 for wild type on cellobiose. Single-colony isolates had no or short lag times on the monosaccharides, while wild type showed 42 ± 4 h on glucose and >80 h on fructose. With good growth on glucose, fructose, and cellobiose, the fructose isolates were chosen for genome sequence-based reverse metabolic engineering. Deletion of a putative transcriptional regulator (Clo1313_1831), which upregulated fructokinase activity, reduced lag time on fructose to 12 h with a growth rate of 0.11 ± 0.01 h-1 and resulted in immediate growth on glucose at 0.24 ± 0.01 h-1 Additional introduction of a G-to-V mutation at position 148 in cbpA resulted in immediate growth on fructose at 0.32 ± 0.03 h-1 These insights can guide engineering of strains for fundamental studies into transport and the upper glycolysis, as well as maximizing product yields in industrial settings.IMPORTANCEC. thermocellum is an important candidate for sustainable and cost-effective production of bioethanol through consolidated bioprocessing. In addition to unsurpassed cellulose deconstruction, industrial application and fundamental studies would benefit from improvement of glucose and fructose consumption. This study demonstrated that C. thermocellum can be evolved for reproducible constitutive growth on glucose or fructose. Subsequent genome sequencing, gene editing, and physiological characterization identified two underlying mutations with a role in (regulation of) transport or metabolism of the hexose sugars. In light of these findings, such mutations have likely (and unknowingly) also occurred in previous studies with C. thermocellum using hexose-based media with possible broad regulatory consequences. By targeted modification of these genes, industrial and research strains of C. thermocellum can be engineered to (i) reduce glucose accumulation, (ii) study cellodextrin transport systems in vivo, (iii) allow experiments at >120 g liter-1 soluble substrate concentration, or (iv) reduce costs for labeling studies.
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Affiliation(s)
- Johannes Yayo
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Teun Kuil
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
| | - Daniel G Olson
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
- The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
- The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Evert K Holwerda
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire, USA
- The Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA
| | - Antonius J A van Maris
- Department of Industrial Biotechnology, School of Engineering Sciences in Chemistry, Biotechnology and Health, KTH Royal Institute of Technology, Stockholm, Sweden
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Mazzoli R, Olson DG, Lynd LR. Construction of lactic acid overproducing Clostridium thermocellum through enhancement of lactate dehydrogenase expression. Enzyme Microb Technol 2020; 141:109645. [PMID: 33051021 DOI: 10.1016/j.enzmictec.2020.109645] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Revised: 07/24/2020] [Accepted: 08/05/2020] [Indexed: 12/24/2022]
Abstract
Rapid expansion of global market of lactic acid (LA) has prompted research towards cheaper and more eco-friendly strategies for its production. Nowadays, LA is produced mainly through fermentation of simple sugars or starchy biomass (e.g. corn) and its price is relatively high. Lignocellulose could be an advantageous alternative feedstock for LA production owing to its high abundance and low cost. However, the most effective natural producers of LA cannot directly ferment lignocellulose. So far, metabolic engineering aimed at developing microorganisms combining efficient LA production and cellulose hydrolysis has been generally based on introducing designer cellulase systems in natural LA producers. In the present study, the approach consisted in improving LA production in the natural cellulolytic bacterium Clostridium thermocellum DSM1313. The expression of the native lactate dehydrogenase was enhanced by functional replacement of its original promoter with stronger ones resulting in a 10-fold increase in specific activity, which resulted in a 2-fold increase of LA yield. It is known that eliminating allosteric regulation can also increase lactic acid production in C. thermocellum, however we were unable to insert strong promoters upstream of the de-regulated ldh gene. A strategy combining these regulations and inactivation of parasitic pathways appears essential for developing a homolactic C. thermocellum.
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Affiliation(s)
- R Mazzoli
- Structural and Functional Biochemistry, Laboratory of Proteomics and Metabolic Engineering of Prokaryotes, Department of Life Sciences and Systems Biology, University of Torino, Via Accademia Albertina 13, 10123, Torino, Italy; Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA.
| | - D G Olson
- Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA
| | - L R Lynd
- Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH, 03755, USA
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15
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Transcriptomic analysis of a Clostridium thermocellum strain engineered to utilize xylose: responses to xylose versus cellobiose feeding. Sci Rep 2020; 10:14517. [PMID: 32884054 PMCID: PMC7471329 DOI: 10.1038/s41598-020-71428-6] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Accepted: 08/10/2020] [Indexed: 12/20/2022] Open
Abstract
Clostridium (Ruminiclostridium) thermocellum is recognized for its ability to ferment cellulosic biomass directly, but it cannot naturally grow on xylose. Recently, C. thermocellum (KJC335) was engineered to utilize xylose through expressing a heterologous xylose catabolizing pathway. Here, we compared KJC335′s transcriptomic responses to xylose versus cellobiose as the primary carbon source and assessed how the bacteria adapted to utilize xylose. Our analyses revealed 417 differentially expressed genes (DEGs) with log2 fold change (FC) >|1| and 106 highly DEGs (log2 FC >|2|). Among the DEGs, two putative sugar transporters, cbpC and cbpD, were up-regulated, suggesting their contribution to xylose transport and assimilation. Moreover, the up-regulation of specific transketolase genes (tktAB) suggests the importance of this enzyme for xylose metabolism. Results also showed remarkable up-regulation of chemotaxis and motility associated genes responding to xylose feeding, as well as widely varying gene expression in those encoding cellulosomal enzymes. For the down-regulated genes, several were categorized in gene ontology terms oxidation–reduction processes, ATP binding and ATPase activity, and integral components of the membrane. This study informs potentially critical, enabling mechanisms to realize the conceptually attractive Next-Generation Consolidated BioProcessing approach where a single species is sufficient for the co-fermentation of cellulose and hemicellulose.
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Garcia S, Thompson RA, Giannone RJ, Dash S, Maranas CD, Trinh CT. Development of a Genome-Scale Metabolic Model of Clostridium thermocellum and Its Applications for Integration of Multi-Omics Datasets and Computational Strain Design. Front Bioeng Biotechnol 2020; 8:772. [PMID: 32974289 PMCID: PMC7471609 DOI: 10.3389/fbioe.2020.00772] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2020] [Accepted: 06/18/2020] [Indexed: 01/29/2023] Open
Abstract
Solving environmental and social challenges such as climate change requires a shift from our current non-renewable manufacturing model to a sustainable bioeconomy. To lower carbon emissions in the production of fuels and chemicals, plant biomass feedstocks can replace petroleum using microorganisms as biocatalysts. The anaerobic thermophile Clostridium thermocellum is a promising bacterium for bioconversion due to its capability to efficiently degrade lignocellulosic biomass. However, the complex metabolism of C. thermocellum is not fully understood, hindering metabolic engineering to achieve high titers, rates, and yields of targeted molecules. In this study, we developed an updated genome-scale metabolic model of C. thermocellum that accounts for recent metabolic findings, has improved prediction accuracy, and is standard-conformant to ensure easy reproducibility. We illustrated two applications of the developed model. We first formulated a multi-omics integration protocol and used it to understand redox metabolism and potential bottlenecks in biofuel (e.g., ethanol) production in C. thermocellum. Second, we used the metabolic model to design modular cells for efficient production of alcohols and esters with broad applications as flavors, fragrances, solvents, and fuels. The proposed designs not only feature intuitive push-and-pull metabolic engineering strategies, but also present novel manipulations around important central metabolic branch-points. We anticipate the developed genome-scale metabolic model will provide a useful tool for system analysis of C. thermocellum metabolism to fundamentally understand its physiology and guide metabolic engineering strategies to rapidly generate modular production strains for effective biosynthesis of biofuels and biochemicals from lignocellulosic biomass.
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Affiliation(s)
- Sergio Garcia
- Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, TN, United States.,Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - R Adam Thompson
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville, TN, United States.,Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - Richard J Giannone
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - Satyakam Dash
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, United States
| | - Costas D Maranas
- Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Department of Chemical Engineering, The Pennsylvania State University, University Park, PA, United States
| | - Cong T Trinh
- Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, TN, United States.,Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN, United States.,Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville, TN, United States.,Oak Ridge National Laboratory, Oak Ridge, TN, United States
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17
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In Vivo Thermodynamic Analysis of Glycolysis in Clostridium thermocellum and Thermoanaerobacterium saccharolyticum Using 13C and 2H Tracers. mSystems 2020; 5:5/2/e00736-19. [PMID: 32184362 PMCID: PMC7380578 DOI: 10.1128/msystems.00736-19] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
Thermodynamics constitutes a key determinant of flux and enzyme efficiency in metabolic networks. Here, we provide new insights into the divergent thermodynamics of the glycolytic pathways of C. thermocellum and T. saccharolyticum, two industrially relevant thermophilic bacteria whose metabolism still is not well understood. We report that while the glycolytic pathway in T. saccharolyticum is as thermodynamically favorable as that found in model organisms, such as E. coli or Saccharomyces cerevisiae, the glycolytic pathway of C. thermocellum operates near equilibrium. The use of a near-equilibrium glycolytic pathway, with potentially increased ATP yield, by this cellulolytic microbe may represent an evolutionary adaptation to growth on cellulose, but it has the drawback of being highly susceptible to product feedback inhibition. The results of this study will facilitate future engineering of high-performance strains capable of transforming cellulosic biomass to biofuels at high yields and titers. Clostridium thermocellum and Thermoanaerobacterium saccharolyticum are thermophilic anaerobic bacteria with complementary metabolic capabilities that utilize distinct glycolytic pathways for the conversion of cellulosic sugars to biofuels. We integrated quantitative metabolomics with 2H and 13C metabolic flux analysis to investigate the in vivo reversibility and thermodynamics of the central metabolic networks of these two microbes. We found that the glycolytic pathway in C. thermocellum operates remarkably close to thermodynamic equilibrium, with an overall drop in Gibbs free energy 5-fold lower than that of T. saccharolyticum or anaerobically grown Escherichia coli. The limited thermodynamic driving force of glycolysis in C. thermocellum could be attributed in large part to the small free energy of the phosphofructokinase reaction producing fructose bisphosphate. The ethanol fermentation pathway was also substantially more reversible in C. thermocellum than in T. saccharolyticum. These observations help explain the comparatively low ethanol titers of C. thermocellum and suggest engineering interventions that can be used to increase its ethanol productivity and glycolytic rate. In addition to thermodynamic analysis, we used our isotope tracer data to reconstruct the T. saccharolyticum central metabolic network, revealing exclusive use of the Embden-Meyerhof-Parnas (EMP) pathway for glycolysis, a bifurcated tricarboxylic acid (TCA) cycle, and a sedoheptulose bisphosphate bypass active within the pentose phosphate pathway. IMPORTANCE Thermodynamics constitutes a key determinant of flux and enzyme efficiency in metabolic networks. Here, we provide new insights into the divergent thermodynamics of the glycolytic pathways of C. thermocellum and T. saccharolyticum, two industrially relevant thermophilic bacteria whose metabolism still is not well understood. We report that while the glycolytic pathway in T. saccharolyticum is as thermodynamically favorable as that found in model organisms, such as E. coli or Saccharomyces cerevisiae, the glycolytic pathway of C. thermocellum operates near equilibrium. The use of a near-equilibrium glycolytic pathway, with potentially increased ATP yield, by this cellulolytic microbe may represent an evolutionary adaptation to growth on cellulose, but it has the drawback of being highly susceptible to product feedback inhibition. The results of this study will facilitate future engineering of high-performance strains capable of transforming cellulosic biomass to biofuels at high yields and titers.
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18
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Usai G, Cirrincione S, Re A, Manfredi M, Pagnani A, Pessione E, Mazzoli R. Clostridium cellulovorans metabolism of cellulose as studied by comparative proteomic approach. J Proteomics 2020; 216:103667. [DOI: 10.1016/j.jprot.2020.103667] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2019] [Revised: 12/31/2019] [Accepted: 01/22/2020] [Indexed: 12/15/2022]
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19
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Koendjbiharie JG, Hon S, Pabst M, Hooftman R, Stevenson DM, Cui J, Amador-Noguez D, Lynd LR, Olson DG, van Kranenburg R. The pentose phosphate pathway of cellulolytic clostridia relies on 6-phosphofructokinase instead of transaldolase. J Biol Chem 2020; 295:1867-1878. [PMID: 31871051 PMCID: PMC7029132 DOI: 10.1074/jbc.ra119.011239] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 12/16/2019] [Indexed: 01/24/2023] Open
Abstract
The genomes of most cellulolytic clostridia do not contain genes annotated as transaldolase. Therefore, for assimilating pentose sugars or for generating C5 precursors (such as ribose) during growth on other (non-C5) substrates, they must possess a pathway that connects pentose metabolism with the rest of metabolism. Here we provide evidence that for this connection cellulolytic clostridia rely on the sedoheptulose 1,7-bisphosphate (SBP) pathway, using pyrophosphate-dependent phosphofructokinase (PPi-PFK) instead of transaldolase. In this reversible pathway, PFK converts sedoheptulose 7-phosphate (S7P) to SBP, after which fructose-bisphosphate aldolase cleaves SBP into dihydroxyacetone phosphate and erythrose 4-phosphate. We show that PPi-PFKs of Clostridium thermosuccinogenes and Clostridium thermocellum indeed can convert S7P to SBP, and have similar affinities for S7P and the canonical substrate fructose 6-phosphate (F6P). By contrast, (ATP-dependent) PfkA of Escherichia coli, which does rely on transaldolase, had a very poor affinity for S7P. This indicates that the PPi-PFK of cellulolytic clostridia has evolved the use of S7P. We further show that C. thermosuccinogenes contains a significant SBP pool, an unusual metabolite that is elevated during growth on xylose, demonstrating its relevance for pentose assimilation. Last, we demonstrate that a second PFK of C. thermosuccinogenes that operates with ATP and GTP exhibits unusual kinetics toward F6P, as it appears to have an extremely high degree of cooperative binding, resulting in a virtual on/off switch for substrate concentrations near its K½ value. In summary, our results confirm the existence of an SBP pathway for pentose assimilation in cellulolytic clostridia.
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Affiliation(s)
| | - Shuen Hon
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755; Center for Bioenergy Innovation, Oak Ridge National Laboratories, Oak Ridge, Tennessee 37830
| | - Martin Pabst
- Cell Systems Engineering, Delft University of Technology, 2629 HZ Delft, The Netherlands
| | - Robert Hooftman
- Laboratory of Microbiology, Wageningen University & Research, 6708 WE Wageningen, The Netherlands
| | - David M Stevenson
- Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Jingxuan Cui
- Center for Bioenergy Innovation, Oak Ridge National Laboratories, Oak Ridge, Tennessee 37830; Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, 03755
| | - Daniel Amador-Noguez
- Center for Bioenergy Innovation, Oak Ridge National Laboratories, Oak Ridge, Tennessee 37830; Department of Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin 53706
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755; Center for Bioenergy Innovation, Oak Ridge National Laboratories, Oak Ridge, Tennessee 37830; Department of Biological Sciences, Dartmouth College, Hanover, New Hampshire, 03755
| | - Daniel G Olson
- Thayer School of Engineering, Dartmouth College, Hanover, New Hampshire 03755; Center for Bioenergy Innovation, Oak Ridge National Laboratories, Oak Ridge, Tennessee 37830
| | - Richard van Kranenburg
- Corbion, 4206 AC Gorinchem, The Netherlands; Laboratory of Microbiology, Wageningen University & Research, 6708 WE Wageningen, The Netherlands.
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Mazzoli R, Olson D. Clostridium thermocellum: A microbial platform for high-value chemical production from lignocellulose. ADVANCES IN APPLIED MICROBIOLOGY 2020; 113:111-161. [PMID: 32948265 DOI: 10.1016/bs.aambs.2020.07.004] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Second generation biorefining, namely fermentation processes based on lignocellulosic feedstocks, has attracted tremendous interest (owing to the large availability and low cost of this biomass) as a strategy to produce biofuels and commodity chemicals that is an alternative to oil refining. However, the innate recalcitrance of lignocellulose has slowed progress toward economically viable processes. Consolidated bioprocessing (CBP), i.e., single-step fermentation of lignocellulose may dramatically reduce the current costs of 2nd generation biorefining. Metabolic engineering has been used as a tool to develop improved microbial strains supporting CBP. Clostridium thermocellum is among the most efficient cellulose degraders isolated so far and one of the most promising host organisms for application of CBP. The development of efficient and reliable genetic tools has allowed significant progress in metabolic engineering of this strain aimed at expanding the panel of growth substrates and improving the production of a number of commodity chemicals of industrial interest such as ethanol, butanol, isobutanol, isobutyl acetate and lactic acid. The present review aims to summarize recent developments in metabolic engineering of this organism which currently represents a reference model for the development of biocatalysts for 2nd generation biorefining.
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Banach A, Ciesielski S, Bacza T, Pieczykolan M, Ziembińska-Buczyńska A. Microbial community composition and methanogens' biodiversity during a temperature shift in a methane fermentation chamber. ENVIRONMENTAL TECHNOLOGY 2019; 40:3252-3263. [PMID: 29683411 DOI: 10.1080/09593330.2018.1468490] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Accepted: 04/17/2018] [Indexed: 06/08/2023]
Abstract
More information on the connection between anaerobic digestion (AD) parameters and composition of the microbial community involved in the AD process is required to gain a better understanding of how a bioreactor functions. The aim of this study was to analyse the composition of microbial communities and the dynamics of methanogens' biodiversity changes during the shift from mesophilic (38°C) to thermophilic (55°C) conditions during biogas production. The total microbial composition was examined via the metagenomic approach based on 16S rRNA gene sequencing, whereas the methanogen communities were analysed using PCR-DGGE (Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis) of mcrA. Even though the temperature is one of the crucial parameters affecting microorganisms involved in the AD process, the results presented here revealed that there were no statistically significant differences in bacterial community composition between the mesophilic and thermophilic phases of the process. The most abundant phyla were found to be Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. However, the methanogens' community genotypic structure as examined by the PCR-DGGE method changed under thermophilic conditions. The temperature had the strongest impact on the archaeal methanogens in the fermentation chamber directly after implementing the temperature shift. A relatively higher biogas yield and average content of CH4 in the produced biogas were observed under thermophilic conditions.
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Affiliation(s)
- Anna Banach
- Environmental Biotechnology Department, Faculty of Power and Environmental Engineering, The Silesian University of Technology , Gliwice , Poland
| | - Sławomir Ciesielski
- Department of Environmental Biotechnology, University of Warmia and Mazury in Olsztyn , Olsztyn , Poland
| | - Tomasz Bacza
- Environmental Biotechnology Department, Faculty of Power and Environmental Engineering, The Silesian University of Technology , Gliwice , Poland
| | - Marek Pieczykolan
- Regional Center for Water and Wastewater Management Co. , Tychy , Poland
| | - Aleksandra Ziembińska-Buczyńska
- Environmental Biotechnology Department, Faculty of Power and Environmental Engineering, The Silesian University of Technology , Gliwice , Poland
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Dash S, Olson DG, Joshua Chan SH, Amador-Noguez D, Lynd LR, Maranas CD. Thermodynamic analysis of the pathway for ethanol production from cellobiose in Clostridium thermocellum. Metab Eng 2019; 55:161-169. [PMID: 31220663 DOI: 10.1016/j.ymben.2019.06.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Revised: 06/01/2019] [Accepted: 06/14/2019] [Indexed: 12/17/2022]
Abstract
Clostridium thermocellum is a candidate for consolidated bioprocessing by carrying out both cellulose solubilization and fermentation. However, despite significant efforts the maximum ethanol titer achieved to date remains below industrially required targets. Several studies have analyzed the impact of increasing ethanol concentration on C. thermocellum's membrane properties, cofactor pool ratios, and altered enzyme regulation. In this study, we explore the extent to which thermodynamic equilibrium limits maximum ethanol titer. We used the max-min driving force (MDF) algorithm (Noor et al., 2014) to identify the range of allowable metabolite concentrations that maintain a negative free energy change for all reaction steps in the pathway from cellobiose to ethanol. To this end, we used a time-series metabolite concentration dataset to flag five reactions (phosphofructokinase (PFK), fructose bisphosphate aldolase (FBA), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), aldehyde dehydrogenase (ALDH) and alcohol dehydrogenase (ADH)) which become thermodynamic bottlenecks under high external ethanol concentrations. Thermodynamic analysis was also deployed in a prospective mode to evaluate genetic interventions which can improve pathway thermodynamics by generating minimal set of reactions or elementary flux modes (EFMs) which possess unique genetic variations while ensuring mass and redox balance with ethanol production. MDF evaluation of all generated (336) EFMs indicated that, i) pyruvate phosphate dikinase (PPDK) has a higher pathway MDF than the malate shunt alternative due to limiting CO2 concentrations under physiological conditions, and ii) NADPH-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPN) can alleviate thermodynamic bottlenecks at high ethanol concentrations due to cofactor modification and reduction in ATP generation. The combination of ATP linked phosphofructokinase (PFK-ATP) and NADPH linked alcohol dehydrogenase (ADH-NADPH) with NADPH linked aldehyde dehydrogenase (ALDH-NADPH) or ferredoxin: NADP + oxidoreductase (NADPH-FNOR) emerges as the best intervention strategy for ethanol production that balances MDF improvements with ATP generation, and appears to functionally reproduce the pathway employed by the ethanologen Thermoanaerobacterium saccharolyticum. Expanding the list of measured intracellular metabolites and improving the quantification accuracy of measurements was found to improve the fidelity of pathway thermodynamics analysis in C. thermocellum. This study demonstrates even before addressing an organism's enzyme kinetics and allosteric regulations, pathway thermodynamics can flag pathway bottlenecks and identify testable strategies for enhancing pathway thermodynamic feasibility and function.
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Affiliation(s)
- Satyakam Dash
- Department of Chemical Engineering, The Pennsylvania State University, University Park, University Park, PA, USA; Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
| | - Daniel G Olson
- Thayer School of Engineering at Dartmouth College, Hanover, NH, USA; Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
| | - Siu Hung Joshua Chan
- Department of Chemical and Biological Engineering, Colorado State University, Fort Collins, CO, USA; Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
| | - Daniel Amador-Noguez
- Department of Bacteriology, University of Wisconsin, Madison, WI, USA; Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
| | - Lee R Lynd
- Thayer School of Engineering at Dartmouth College, Hanover, NH, USA; Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
| | - Costas D Maranas
- Department of Chemical Engineering, The Pennsylvania State University, University Park, University Park, PA, USA; Center for Bioenergy Innovation, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
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Aburaya S, Aoki W, Kuroda K, Minakuchi H, Ueda M. Temporal proteome dynamics of Clostridium cellulovorans cultured with major plant cell wall polysaccharides. BMC Microbiol 2019; 19:118. [PMID: 31159733 PMCID: PMC6547498 DOI: 10.1186/s12866-019-1480-0] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 05/07/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Clostridium cellulovorans is a mesophilic, cellulosome-producing bacterium containing 57 genomic cellulosomal enzyme-encoding genes. In addition to cellulosomal proteins, C. cellulovorans also secretes non-cellulosomal proteins to degrade plant cell wall polysaccharides. Unlike other cellulosome-producing Clostridium species, C. cellulovorans can metabolize all major plant cell wall polysaccharides (cellulose, hemicelluloses, and pectins). In this study, we performed a temporal proteome analysis of C. cellulovorans to reveal strategies underlying plant cell wall polysaccharide degradation. RESULTS We cultured C. cellulovorans with five different carbon sources (glucose, cellulose, xylan, galactomannan, and pectin) and performed proteome analysis on cellular and secreted proteins. In total, we identified 1895 cellular proteins and 875 secreted proteins. The identified unique carbohydrate-degrading enzymes corresponding to each carbon source were annotated to have specific activity against each carbon source. However, we identified pectate lyase as a unique enzyme in C. cellulovorans cultivated on xylan, which was not previously associated with xylan degradation. We performed k-means clustering analysis for elucidation of temporal changes of the cellular and secreted proteins in each carbon sources. We found that cellular proteins in most of the k-means clusters are involved in carbohydrate metabolism, amino acid metabolism, translation, or membrane transport. When xylan and pectin were used as the carbon sources, the most increasing k-means cluster contained proteins involved in the metabolism of cofactors and vitamins. In case of secreted proteins of C. cellulovorans cultured either on cellulose or xylan, galactomannan, and pectin, the clusters with the most increasing trend contained either 25 cellulosomal proteins and five non-cellulosomal proteins or 8-19 cellulosomal proteins and 9-16 non-cellulosomal proteins, respectively. These differences might reflect mechanisms for degrading cellulose of other carbon source. Co-abundance analysis of the secreted proteins revealed that proteases and protease inhibitors accumulated coordinately. This observation implies that the secreted protease inhibitors and proteases protect carbohydrate-degrading enzymes from an attack from the plant. CONCLUSION In this study, we clarified, for the first time, the temporal proteome dynamics of cellular and secreted proteins in C. cellulovorans. This data will be valuable in understanding strategies employed by C. cellulovorans for degrading major plant cell wall polysaccharides.
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Affiliation(s)
- Shunsuke Aburaya
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, Japan.,Research Fellow of the Japan Society for the Promotion of Science, Sakyo-ku, Kyoto, Japan
| | - Wataru Aoki
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, Japan.,Kyoto Integrated Science and Technology Bio-Analysis Center, Shimogyo-ku, Kyoto, Japan.,JST-PRESTO, Chiyoda-ku, Tokyo, Japan
| | - Kouichi Kuroda
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, Japan
| | - Hiroshi Minakuchi
- Kyoto-monotech, 1095, Shuzei-cho, Kamigyo-ku, Kyoto-shi, Kyoto, 602-8155, Japan
| | - Mitsuyoshi Ueda
- Division of Applied Life Sciences, Graduate School of Agriculture, Kyoto University, Sakyo-ku, Kyoto, Japan. .,Kyoto Integrated Science and Technology Bio-Analysis Center, Shimogyo-ku, Kyoto, Japan. .,JST-PRESTO, Chiyoda-ku, Tokyo, Japan.
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Froese A, Schellenberg J, Sparling R. Enhanced depolymerization and utilization of raw lignocellulosic material by co-cultures of Ruminiclostridium thermocellum with hemicellulose-utilizing partners. Can J Microbiol 2019; 65:296-307. [PMID: 30608879 DOI: 10.1139/cjm-2018-0535] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Ruminiclostridium thermocellum is one of the most promising candidates for consolidated bioprocessing (CBP) of low-cost lignocellulosic materials to biofuels but it still shows poor performance in its ability to deconstruct untreated lignocellulosic substrates. One promising approach to increase R. thermocellum's rate of hydrolysis is to co-culture this cellulose-specialist with partners that possess synergistic hydrolysis enzymes and metabolic capabilities. We have created co-cultures of R. thermocellum with two hemicellulose utilizers, Ruminiclostridium stercorarium and Thermoanaerobacter thermohydrosulfuricus, both of which secrete xylanolytic enzymes and utilize the pentose oligo- and monosaccharides that inhibit R. thermocellum's hydrolysis and metabolism. When grown on milled wheat straw, the co-cultures were able to solubilize up to 58% more of the total polysaccharides than the R. thermocellum mono-culture control. Repeated passaging of the co-cultures on wheat straw yielded stable populations with reduced R. thermocellum cell numbers, indicating competition for cellodextrins released from cellulose hydrolysis, although these stabilized co-cultures were still able to outperform the mono-culture controls. Repeated passaging on Avicel cellulose also yielded stable populations. Overall, the observed synergism suggests that co-culturing R. thermocellum with other members is a viable option for increasing the rate and extent of untreated lignocellulose deconstruction by R. thermocellum for CBP purposes.
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Affiliation(s)
- Alan Froese
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.,Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
| | - John Schellenberg
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.,Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
| | - Richard Sparling
- Department of Microbiology, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
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Characterization of the Clostridium thermocellum AdhE, NfnAB, ferredoxin and Pfor proteins for their ability to support high titer ethanol production in Thermoanaerobacterium saccharolyticum. Metab Eng 2018; 51:32-42. [PMID: 30218716 DOI: 10.1016/j.ymben.2018.09.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2018] [Revised: 08/21/2018] [Accepted: 09/11/2018] [Indexed: 12/17/2022]
Abstract
The thermophilic anaerobes Thermoanaerobacterium saccharolyticum and Clostridium thermocellum are good candidates for lignocellulosic ethanol production. T. saccharolyticum has been successfully engineered to produce ethanol at high titer (70 g/L). The maximum ethanol titer of engineered strains of C. thermocellum is only 25 g/L. We hypothesize that one or more of the enzymes in the ethanol production pathway in C. thermocellum is not adequate for ethanol production at high titer. In this study, we focused on the enzymes responsible for the part of the ethanol production pathway from pyruvate to ethanol. In T. saccharolyticum, we replaced all of the genes encoding proteins in this pathway with their homologs from C. thermocellum and examined what combination of gene replacements restricted ethanol titer. We found that a pathway consisting of Ct_nfnAB, Ct_fd, Ct_adhE and Ts_pforA was sufficient to support ethanol titer greater than 50 g/L, however replacement of Ts_pforA by Ct_pfor1 dramatically decreased the maximum ethanol titer to 14 g/L. We then demonstrated that the reason for reduced ethanol production is that the Ct_pfor1 is inhibited by accumulation of ethanol and NADH, while Ts_pforA is not.
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26
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Aikawa S, Baramee S, Sermsathanaswadi J, Thianheng P, Tachaapaikoon C, Shikata A, Waeonukul R, Pason P, Ratanakhanokchai K, Kosugi A. Characterization and high-quality draft genome sequence of Herbivorax saccincola A7, an anaerobic, alkaliphilic, thermophilic, cellulolytic, and xylanolytic bacterium. Syst Appl Microbiol 2018; 41:261-269. [DOI: 10.1016/j.syapm.2018.01.010] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2017] [Revised: 01/24/2018] [Accepted: 01/25/2018] [Indexed: 10/18/2022]
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27
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Daas MJA, Nijsse B, van de Weijer AHP, Groenendaal BWAJ, Janssen F, van der Oost J, van Kranenburg R. Engineering Geobacillus thermodenitrificans to introduce cellulolytic activity; expression of native and heterologous cellulase genes. BMC Biotechnol 2018; 18:42. [PMID: 29945583 PMCID: PMC6020330 DOI: 10.1186/s12896-018-0453-y] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2017] [Accepted: 06/14/2018] [Indexed: 11/28/2022] Open
Abstract
Background Consolidated bioprocessing (CBP) is a cost-effective approach for the conversion of lignocellulosic biomass to biofuels and biochemicals. The enzymatic conversion of cellulose to glucose requires the synergistic action of three types of enzymes: exoglucanases, endoglucanases and β-glucosidases. The thermophilic, hemicellulolytic Geobacillus thermodenitrificans T12 was shown to harbor desired features for CBP, although it lacks the desired endo and exoglucanases required for the conversion of cellulose. Here, we report the expression of both endoglucanase and exoglucanase encoding genes by G. thermodenitrificans T12, in an initial attempt to express cellulolytic enzymes that complement the enzymatic machinery of this strain. Results A metagenome screen was performed on 73 G. thermodenitrificans strains using HMM profiles of all known CAZy families that contain endo and/or exoglucanases. Two putative endoglucanases, GE39 and GE40, belonging to glucoside hydrolase family 5 (GH5) were isolated and expressed in both E. coli and G. thermodenitrificans T12. Structure modeling of GE39 revealed a folding similar to a GH5 exo-1,3-β-glucanase from S. cerevisiae. However, we determined GE39 to be a β-xylosidase having pronounced activity towards p-nitrophenyl-β-d-xylopyranoside. Structure modelling of GE40 revealed its protein architecture to be similar to a GH5 endoglucanase from B. halodurans, and its endoglucanase activity was confirmed by enzymatic activity against 2-hydroxyethylcellulose, carboxymethylcellulose and barley β-glucan. Additionally, we introduced expression constructs into T12 containing Geobacillus sp. 70PC53 endoglucanase gene celA and both endoglucanase genes (M1 and M2) from Geobacillus sp. WSUCF1. Finally, we introduced expression constructs into T12 containing the C. thermocellum exoglucanases celK and celS genes and the endoglucanase celC gene. Conclusions We identified a novel G. thermodenitrificans β-xylosidase (GE39) and a novel endoglucanase (GE40) using a metagenome screen based on multiple HMM profiles. We successfully expressed both genes in E. coli and functionally expressed the GE40 endoglucanase in G. thermodenitrificans T12. Additionally, the heterologous production of active CelK, a C. thermocellum derived exoglucanase, and CelA, a Geobacillus derived endoglucanase, was demonstrated with strain T12. The native hemicellulolytic activity and the heterologous cellulolytic activity described in this research provide a good basis for the further development of G. thermodenitrificans T12 as a host for consolidated bioprocessing. Electronic supplementary material The online version of this article (10.1186/s12896-018-0453-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Martinus J A Daas
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands
| | - Bart Nijsse
- Laboratory of Systems and Synthetic Biology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands
| | | | - Bart W A J Groenendaal
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands
| | - Fons Janssen
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands
| | - John van der Oost
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands
| | - Richard van Kranenburg
- Laboratory of Microbiology, Wageningen University, Stippeneng 4, 6708, WE, Wageningen, The Netherlands. .,Corbion, Arkelsedijk 46, 4206, AC, Gorinchem, The Netherlands.
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28
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Investigating the Central Metabolism of Clostridium thermosuccinogenes. Appl Environ Microbiol 2018; 84:AEM.00363-18. [PMID: 29678919 DOI: 10.1128/aem.00363-18] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2018] [Accepted: 04/15/2018] [Indexed: 01/28/2023] Open
Abstract
Clostridium thermosuccinogenes is a thermophilic anaerobic bacterium able to convert various carbohydrates to succinate and acetate as main fermentation products. Genomes of the four publicly available strains have been sequenced, and the genome of the type strain has been closed. The annotated genomes were used to reconstruct the central metabolism, and enzyme assays were used to validate annotations and to determine cofactor specificity. The genes were identified for the pathways to all fermentation products, as well as for the Embden-Meyerhof-Parnas pathway and the pentose phosphate pathway. Notably, a candidate transaldolase was lacking, and transcriptomics during growth on glucose versus that on xylose did not provide any leads to potential transaldolase genes or alternative pathways connecting the C5 with the C3/C6 metabolism. Enzyme assays showed xylulokinase to prefer GTP over ATP, which could be of importance for engineering xylose utilization in related thermophilic species of industrial relevance. Furthermore, the gene responsible for malate dehydrogenase was identified via heterologous expression in Escherichia coli and subsequent assays with the cell extract, which has proven to be a simple and powerful method for the basal characterization of thermophilic enzymes.IMPORTANCE Running industrial fermentation processes at elevated temperatures has several advantages, including reduced cooling requirements, increased reaction rates and solubilities, and a possibility to perform simultaneous saccharification and fermentation of a pretreated biomass. Most studies with thermophiles so far have focused on bioethanol production. Clostridium thermosuccinogenes seems an attractive production organism for organic acids, succinic acid in particular, from lignocellulosic biomass-derived sugars. This study provides valuable insights into its central metabolism and GTP and PPi cofactor utilization.
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29
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Whitham JM, Moon JW, Rodriguez M, Engle NL, Klingeman DM, Rydzak T, Abel MM, Tschaplinski TJ, Guss AM, Brown SD. Clostridium thermocellum LL1210 pH homeostasis mechanisms informed by transcriptomics and metabolomics. BIOTECHNOLOGY FOR BIOFUELS 2018; 11:98. [PMID: 29632556 PMCID: PMC5887222 DOI: 10.1186/s13068-018-1095-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2017] [Accepted: 03/24/2018] [Indexed: 05/21/2023]
Abstract
BACKGROUND Clostridium (Ruminiclostridium) thermocellum is a model fermentative anaerobic thermophile being studied and engineered for consolidated bioprocessing of lignocellulosic feedstocks into fuels and chemicals. Engineering efforts have resulted in significant improvements in ethanol yields and titers although further advances are required to make the bacterium industry-ready. For instance, fermentations at lower pH could enable co-culturing with microbes that have lower pH optima, augment productivity, and reduce buffering cost. C. thermocellum is typically grown at neutral pH, and little is known about its pH limits or pH homeostasis mechanisms. To better understand C. thermocellum pH homeostasis we grew strain LL1210 (C. thermocellum DSM1313 Δhpt ΔhydG Δldh Δpfl Δpta-ack), currently the highest ethanol producing strain of C. thermocellum, at different pH values in chemostat culture and applied systems biology tools. RESULTS Clostridium thermocellum LL1210 was found to be growth-limited below pH 6.24 at a dilution rate of 0.1 h-1. F1F0-ATPase gene expression was upregulated while many ATP-utilizing enzymes and pathways were downregulated at pH 6.24. These included most flagella biosynthesis genes, genes for chemotaxis, and other motility-related genes (> 50) as well as sulfate transport and reduction, nitrate transport and nitrogen fixation, and fatty acid biosynthesis genes. Clustering and enrichment of differentially expressed genes at pH values 6.48, pH 6.24 and pH 6.12 (washout conditions) compared to pH 6.98 showed inverse differential expression patterns between the F1F0-ATPase and genes for other ATP-utilizing enzymes. At and below pH 6.24, amino acids including glutamate and valine; long-chain fatty acids, their iso-counterparts and glycerol conjugates; glycolysis intermediates 3-phosphoglycerate, glucose 6-phosphate, and glucose accumulated intracellularly. Glutamate was 267 times more abundant in cells at pH 6.24 compared to pH 6.98, and intercellular concentration reached 1.8 μmol/g pellet at pH 5.80 (stopped flow). CONCLUSIONS Clostridium thermocellum LL1210 can grow under slightly acidic conditions, similar to limits reported for other strains. This foundational study provides a detailed characterization of a relatively acid-intolerant bacterium and provides genetic targets for strain improvement. Future studies should examine adding gene functions used by more acid-tolerant bacteria for improved pH homeostasis at acidic pH values.
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Affiliation(s)
- Jason M. Whitham
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Ji-Won Moon
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Miguel Rodriguez
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Nancy L. Engle
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Dawn M. Klingeman
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Thomas Rydzak
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
- Present Address: Department of Biological Science, University of Calgary, Calgary, AB T2N 1N4 Canada
| | - Malaney M. Abel
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Timothy J. Tschaplinski
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Adam M. Guss
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
| | - Steven D. Brown
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- BioEnergy Science Center, National Laboratory, Oak Ridge, TN USA
- Present Address: LanzaTech, Inc., Skokie, IL USA
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Li S, Shao N, Luo Y, Liu H, Cai S, Dong X. Transcriptome and Zymogram Analyses Reveal a Cellobiose-Dose Related Reciprocal Regulatory Effect on Cellulase Synthesis in Cellulosilyticum ruminicola H1. Front Microbiol 2017; 8:2497. [PMID: 29312203 PMCID: PMC5733062 DOI: 10.3389/fmicb.2017.02497] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2017] [Accepted: 11/30/2017] [Indexed: 11/21/2022] Open
Abstract
The rumen bacterium Cellulosilyticum ruminicola H1 efficiently hydrolyzes cellulose. To gain insights into the regulatory mechanisms of cellulase synthesis, comparative transcriptome analysis was conducted for cultures grown on 2% filter paper, 0.5 and 0.05% cellobiose, and 0.5% birchwood xylan. It was found that cellulose induced a majority of (hemi)cellulases, including 33 cellulases and a cellulosomal scaffoldin (1.3- to 22.7-fold); seven endoxylanases, two mannanases, and two pectatelyases (2- to 16-fold); and pyruvate formate-lyase (PFL, 1.5- to 7-fold). Noticeably, 3- and 2.5-fold increased transcription of a cellobiohydrolase and the cellulosomal scaffoldin precursor were detected in 0.05% than in 0.5% cellobiose. Consistently, 9- and 4-fold higher specific cellobiohydrolase activities were detected in the filter paper and 0.05% cellobiose culture. SDS- and native-PAGE zymograms of cellulose-enriched proteins from the filter paper culture displayed cellulase activities, and cellulolytic “complexes” were enriched from the filter paper- and 0.05% cellobiose-cultures, but not from the 0.5% cellobiose culture. LC-MS/MS identified the cellulosomal scaffoldin precursor in the “complexes” in addition to cellulase, hemicellulase, and PFL proteins. The addition of 0.5% cellobiose, but not 0.05% cellobiose remarkably inhibited strain H1 to degrade filter paper. Therefore, this work reveals a cellobiose-dose related regulatory mechanism of cellulase synthesis by lower for induction and higher for repression, which has extended our understanding of the regulation of microbial cellulase synthesis.
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Affiliation(s)
- Shanzhen Li
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,State Key Laboratory of Microbial Resources, University of Chinese Academy of Sciences, Beijing, China
| | - Nana Shao
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China.,State Key Laboratory of Microbial Resources, University of Chinese Academy of Sciences, Beijing, China
| | - Yuanming Luo
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Hongcan Liu
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Shichun Cai
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
| | - Xiuzhu Dong
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing, China
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Yoav S, Barak Y, Shamshoum M, Borovok I, Lamed R, Dassa B, Hadar Y, Morag E, Bayer EA. How does cellulosome composition influence deconstruction of lignocellulosic substrates in Clostridium ( Ruminiclostridium) thermocellum DSM 1313? BIOTECHNOLOGY FOR BIOFUELS 2017; 10:222. [PMID: 28932263 PMCID: PMC5604425 DOI: 10.1186/s13068-017-0909-7] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/08/2017] [Accepted: 09/07/2017] [Indexed: 05/23/2023]
Abstract
BACKGROUND Bioethanol production processes involve enzymatic hydrolysis of pretreated lignocellulosic biomass into fermentable sugars. Due to the relatively high cost of enzyme production, the development of potent and cost-effective cellulolytic cocktails is critical for increasing the cost-effectiveness of bioethanol production. In this context, the multi-protein cellulolytic complex of Clostridium (Ruminiclostridium) thermocellum, the cellulosome, was studied here. C. thermocellum is known to assemble cellulosomes of various subunit (enzyme) compositions, in response to the available carbon source. In the current study, different carbon sources were used, and their influence on both cellulosomal composition and the resultant activity was investigated. RESULTS Glucose, cellobiose, microcrystalline cellulose, alkaline-pretreated switchgrass, alkaline-pretreated corn stover, and dilute acid-pretreated corn stover were used as sole carbon sources in the growth media of C. thermocellum strain DSM 1313. The purified cellulosomes were compared for their activity on selected cellulosic substrates. Interestingly, cellulosomes derived from cells grown on lignocellulosic biomass showed no advantage in hydrolyzing the original carbon source used for their production. Instead, microcrystalline cellulose- and glucose-derived cellulosomes were equal or superior in their capacity to deconstruct lignocellulosic biomass. Mass spectrometry analysis revealed differential composition of catalytic and structural subunits (scaffoldins) in the different cellulosome samples. The most abundant catalytic subunits in all cellulosome types include Cel48S, Cel9K, Cel9Q, Cel9R, and Cel5G. Microcrystalline cellulose- and glucose-derived cellulosome samples showed higher endoglucanase-to-exoglucanase ratios and higher catalytic subunit-per-scaffoldin ratios compared to lignocellulose-derived cellulosome types. CONCLUSION The results reported here highlight the finding that cellulosomes derived from cells grown on glucose and microcrystalline cellulose are more efficient in their action on cellulosic substrates than other cellulosome preparations. These results should be considered in the future development of C. thermocellum-based cellulolytic cocktails, designer cellulosomes, or engineering of improved strains for deconstruction of lignocellulosic biomass.
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Affiliation(s)
- Shahar Yoav
- Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture, Food and Environment, The Advanced School for Environmental Studies, The Hebrew University of Jerusalem, 76100 Rehovot, Israel
- Designer Energy Ltd, 2 Bergman Street, Rehovot, Israel
| | - Yoav Barak
- Bio-Nano Unit, Chemical Research Support, The Weizmann Institute of Science, 761000 Rehovot, Israel
| | - Melina Shamshoum
- Department of Biomolecular Sciences, The Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Ilya Borovok
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Israel
| | - Raphael Lamed
- Department of Molecular Microbiology and Biotechnology, Tel Aviv University, Ramat Aviv, Israel
| | - Bareket Dassa
- Department of Biomolecular Sciences, The Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Yitzhak Hadar
- Department of Plant Pathology and Microbiology, Robert H. Smith Faculty of Agriculture, Food and Environment, The Advanced School for Environmental Studies, The Hebrew University of Jerusalem, 76100 Rehovot, Israel
| | - Ely Morag
- Department of Biomolecular Sciences, The Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Edward A. Bayer
- Department of Biomolecular Sciences, The Weizmann Institute of Science, 76100 Rehovot, Israel
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32
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Thompson RA, Trinh CT. Overflow metabolism and growth cessation in Clostridium thermocellum DSM1313 during high cellulose loading fermentations. Biotechnol Bioeng 2017; 114:2592-2604. [PMID: 28671264 DOI: 10.1002/bit.26374] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2017] [Revised: 06/25/2017] [Accepted: 06/27/2017] [Indexed: 12/31/2022]
Abstract
As a model thermophilic bacterium for the production of second-generation biofuels, the metabolism of Clostridium thermocellum has been widely studied. However, most studies have characterized C. thermocellum metabolism for growth at relatively low substrate concentrations. This outlook is not industrially relevant, however, as commercial viability requires substrate loadings of at least 100 g/L cellulosic materials. Recently, a wild-type C. thermocellum DSM1313 was cultured on high cellulose loading batch fermentations and reported to produce a wide range of fermentative products not seen at lower substrate concentrations, opening the door for a more in-depth analysis of how this organism will behave in industrially relevant conditions. In this work, we elucidated the interconnectedness of overflow metabolism and growth cessation in C. thermocellum during high cellulose loading batch fermentations (100 g/L). Metabolic flux and thermodynamic analyses suggested that hydrogen and formate accumulation perturbed the complex redox metabolism and limited conversion of pyruvate to acetyl-CoA conversion, likely leading to overflow metabolism and growth cessation in C. thermocellum. Pyruvate formate lyase (PFL) acts as an important redox valve and its flux is inhibited by formate accumulation. Finally, we demonstrated that manipulation of fermentation conditions to alleviate hydrogen accumulation could dramatically alter the fate of pyruvate, providing valuable insight into process design for enhanced C. thermocellum production of chemicals and biofuels. Biotechnol. Bioeng. 2017;114: 2592-2604. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- R Adam Thompson
- Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville and Oak Ridge National Laboratory, Oak Ridge, Tennessee.,BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee
| | - Cong T Trinh
- Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville and Oak Ridge National Laboratory, Oak Ridge, Tennessee.,BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee.,Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, Tennessee
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33
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Dash S, Khodayari A, Zhou J, Holwerda EK, Olson DG, Lynd LR, Maranas CD. Development of a core Clostridium thermocellum kinetic metabolic model consistent with multiple genetic perturbations. BIOTECHNOLOGY FOR BIOFUELS 2017; 10:108. [PMID: 28469704 PMCID: PMC5414155 DOI: 10.1186/s13068-017-0792-2] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Accepted: 04/18/2017] [Indexed: 06/07/2023]
Abstract
BACKGROUND Clostridium thermocellum is a Gram-positive anaerobe with the ability to hydrolyze and metabolize cellulose into biofuels such as ethanol, making it an attractive candidate for consolidated bioprocessing (CBP). At present, metabolic engineering in C. thermocellum is hindered due to the incomplete description of its metabolic repertoire and regulation within a predictive metabolic model. Genome-scale metabolic (GSM) models augmented with kinetic models of metabolism have been shown to be effective at recapitulating perturbed metabolic phenotypes. RESULTS In this effort, we first update a second-generation genome-scale metabolic model (iCth446) for C. thermocellum by correcting cofactor dependencies, restoring elemental and charge balances, and updating GAM and NGAM values to improve phenotype predictions. The iCth446 model is next used as a scaffold to develop a core kinetic model (k-ctherm118) of the C. thermocellum central metabolism using the Ensemble Modeling (EM) paradigm. Model parameterization is carried out by simultaneously imposing fermentation yield data in lactate, malate, acetate, and hydrogen production pathways for 19 measured metabolites spanning a library of 19 distinct single and multiple gene knockout mutants along with 18 intracellular metabolite concentration data for a Δgldh mutant and ten experimentally measured Michaelis-Menten kinetic parameters. CONCLUSIONS The k-ctherm118 model captures significant metabolic changes caused by (1) nitrogen limitation leading to increased yields for lactate, pyruvate, and amino acids, and (2) ethanol stress causing an increase in intracellular sugar phosphate concentrations (~1.5-fold) due to upregulation of cofactor pools. Robustness analysis of k-ctherm118 alludes to the presence of a secondary activity of ketol-acid reductoisomerase and possible regulation by valine and/or leucine pool levels. In addition, cross-validation and robustness analysis allude to missing elements in k-ctherm118 and suggest additional experiments to improve kinetic model prediction fidelity. Overall, the study quantitatively assesses the advantages of EM-based kinetic modeling towards improved prediction of C. thermocellum metabolism and develops a predictive kinetic model which can be used to design biofuel-overproducing strains.
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Affiliation(s)
- Satyakam Dash
- Department of Chemical Engineering, The Pennsylvania State University, 126 Land and Water Research Building, University Park, PA 16802 USA
| | - Ali Khodayari
- Department of Chemical Engineering, The Pennsylvania State University, 126 Land and Water Research Building, University Park, PA 16802 USA
| | - Jilai Zhou
- Thayer School of Engineering at Dartmouth College, Hanover, NH USA
| | | | - Daniel G. Olson
- Thayer School of Engineering at Dartmouth College, Hanover, NH USA
| | - Lee R. Lynd
- Thayer School of Engineering at Dartmouth College, Hanover, NH USA
| | - Costas D. Maranas
- Department of Chemical Engineering, The Pennsylvania State University, 126 Land and Water Research Building, University Park, PA 16802 USA
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34
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Understanding aerobic/anaerobic metabolism in Caldibacillus debilis through a comparison with model organisms. Syst Appl Microbiol 2017; 40:245-253. [PMID: 28527624 DOI: 10.1016/j.syapm.2017.03.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2016] [Revised: 03/15/2017] [Accepted: 03/20/2017] [Indexed: 11/20/2022]
Abstract
Caldibacillus debilis GB1 is a facultative anaerobe isolated from a thermophilic aero-tolerant cellulolytic enrichment culture. There is a lack of representative proteomes of facultative anaerobic thermophilic Bacillaceae, exploring aerobic/anaerobic expression. The C. debilis GB1 genome was sequenced and annotated, and the proteome characterized under aerobic and anaerobic conditions while grown on cellobiose. The draft sequence of C. debilis GB1 contains a 3,340,752 bp chromosome and a 5,386 bp plasmid distributed over 49 contigs. Two-dimensional liquid chromatography mass spectrometry/mass spectrometry was used with Isobaric Tags for Relative and Absolute Quantification (iTRAQ) to compare protein expression profiles, focusing on energy production and conversion pathways. Under aerobic conditions, proteins in glycolysis and pyruvate fermentation pathways were down-regulated. Simultaneously, proteins within the tricarboxylic acid cycle, pyruvate dehydrogenase, the electron transport chain, and oxygen scavenging pathways showed increased amounts. Under anaerobic conditions, protein levels in fermentation pathways were consistent with the generated end-products: formate, acetate, ethanol, lactate, and CO2. Under aerobic conditions CO2 and acetate production was consistent with incomplete respiration. Through a direct comparison with gene expression profiles from Escherichia coli, we show that global regulation of core metabolism pathways is similar in thermophilic and mesophilic facultative anaerobes of the Phylum Proteobacteria and Firmicutes.
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35
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Rydzak T, Garcia D, Stevenson DM, Sladek M, Klingeman DM, Holwerda EK, Amador-Noguez D, Brown SD, Guss AM. Deletion of Type I glutamine synthetase deregulates nitrogen metabolism and increases ethanol production in Clostridium thermocellum. Metab Eng 2017; 41:182-191. [PMID: 28400329 DOI: 10.1016/j.ymben.2017.04.002] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 03/27/2017] [Accepted: 04/07/2017] [Indexed: 12/25/2022]
Abstract
Clostridium thermocellum rapidly deconstructs cellulose and ferments resulting hydrolysis products into ethanol and other products, and is thus a promising platform organism for the development of cellulosic biofuel production via consolidated bioprocessing. While recent metabolic engineering strategies have targeted eliminating canonical fermentation products (acetate, lactate, formate, and H2), C. thermocellum also secretes amino acids, which has limited ethanol yields in engineered strains to approximately 70% of the theoretical maximum. To investigate approaches to decrease amino acid secretion, we attempted to reduce ammonium assimilation by deleting the Type I glutamine synthetase (glnA) in an essentially wild type strain of C. thermocellum. Deletion of glnA reduced levels of secreted valine and total amino acids by 53% and 44% respectively, and increased ethanol yields by 53%. RNA-seq analysis revealed that genes encoding the RNF-complex were more highly expressed in ΔglnA and may have a role in improving NADH-availability for ethanol production. While a significant up-regulation of genes involved in nitrogen assimilation and urea uptake suggested that deletion of glnA induces a nitrogen starvation response, metabolomic analysis showed an increase in intracellular glutamine levels indicative of nitrogen-rich conditions. We propose that deletion of glnA causes deregulation of nitrogen metabolism, leading to overexpression of nitrogen metabolism genes and, in turn, elevated glutamine levels. Here we demonstrate that perturbation of nitrogen assimilation is a promising strategy to redirect flux from the production of nitrogenous compounds toward biofuels in C. thermocellum.
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Affiliation(s)
- Thomas Rydzak
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - David Garcia
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - David M Stevenson
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, United States
| | - Margaret Sladek
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - Dawn M Klingeman
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - Evert K Holwerda
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; Thayer School of Engineering at Dartmouth College, Hanover, NH, United States
| | - Daniel Amador-Noguez
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI, United States
| | - Steven D Brown
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, United States
| | - Adam M Guss
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, United States; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, United States.
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36
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Dumitrache A, Klingeman DM, Natzke J, Rodriguez M, Giannone RJ, Hettich RL, Davison BH, Brown SD. Specialized activities and expression differences for Clostridium thermocellum biofilm and planktonic cells. Sci Rep 2017; 7:43583. [PMID: 28240279 PMCID: PMC5327387 DOI: 10.1038/srep43583] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2016] [Accepted: 01/25/2017] [Indexed: 01/01/2023] Open
Abstract
Clostridium (Ruminiclostridium) thermocellum is a model organism for its ability to deconstruct plant biomass and convert the cellulose into ethanol. The bacterium forms biofilms adherent to lignocellulosic feedstocks in a continuous cell-monolayer in order to efficiently break down and uptake cellulose hydrolysates. We developed a novel bioreactor design to generate separate sessile and planktonic cell populations for omics studies. Sessile cells had significantly greater expression of genes involved in catabolism of carbohydrates by glycolysis and pyruvate fermentation, ATP generation by proton gradient, the anabolism of proteins and lipids and cellular functions critical for cell division consistent with substrate replete conditions. Planktonic cells had notably higher gene expression for flagellar motility and chemotaxis, cellulosomal cellulases and anchoring scaffoldins, and a range of stress induced homeostasis mechanisms such as oxidative stress protection by antioxidants and flavoprotein co-factors, methionine repair, Fe-S cluster assembly and repair in redox proteins, cell growth control through tRNA thiolation, recovery of damaged DNA by nucleotide excision repair and removal of terminal proteins by proteases. This study demonstrates that microbial attachment to cellulose substrate produces widespread gene expression changes for critical functions of this organism and provides physiological insights for two cells populations relevant for engineering of industrially-ready phenotypes.
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Affiliation(s)
- Alexandru Dumitrache
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Dawn M Klingeman
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Jace Natzke
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Miguel Rodriguez
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Richard J Giannone
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Robert L Hettich
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Brian H Davison
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
| | - Steven D Brown
- BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, U.S.A
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37
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Verbeke TJ, Giannone RJ, Klingeman DM, Engle NL, Rydzak T, Guss AM, Tschaplinski TJ, Brown SD, Hettich RL, Elkins JG. Pentose sugars inhibit metabolism and increase expression of an AgrD-type cyclic pentapeptide in Clostridium thermocellum. Sci Rep 2017; 7:43355. [PMID: 28230109 PMCID: PMC5322536 DOI: 10.1038/srep43355] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 01/18/2017] [Indexed: 12/22/2022] Open
Abstract
Clostridium thermocellum could potentially be used as a microbial biocatalyst to produce renewable fuels directly from lignocellulosic biomass due to its ability to rapidly solubilize plant cell walls. While the organism readily ferments sugars derived from cellulose, pentose sugars from xylan are not metabolized. Here, we show that non-fermentable pentoses inhibit growth and end-product formation during fermentation of cellulose-derived sugars. Metabolomic experiments confirmed that xylose is transported intracellularly and reduced to the dead-end metabolite xylitol. Comparative RNA-seq analysis of xylose-inhibited cultures revealed several up-regulated genes potentially involved in pentose transport and metabolism, which were targeted for disruption. Deletion of the ATP-dependent transporter, CbpD partially alleviated xylose inhibition. A putative xylitol dehydrogenase, encoded by Clo1313_0076, was also deleted resulting in decreased total xylitol production and yield by 41% and 46%, respectively. Finally, xylose-induced inhibition corresponds with the up-regulation and biogenesis of a cyclical AgrD-type, pentapeptide. Medium supplementation with the mature cyclical pentapeptide also inhibits bacterial growth. Together, these findings provide new foundational insights needed for engineering improved pentose utilizing strains of C. thermocellum and reveal the first functional Agr-type cyclic peptide to be produced by a thermophilic member of the Firmicutes.
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Affiliation(s)
- Tobin J Verbeke
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Richard J Giannone
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Dawn M Klingeman
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Nancy L Engle
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Thomas Rydzak
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Adam M Guss
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Timothy J Tschaplinski
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Steven D Brown
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Robert L Hettich
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - James G Elkins
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA.,Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
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38
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Taillefer M, Sparling R. Glycolysis as the Central Core of Fermentation. ADVANCES IN BIOCHEMICAL ENGINEERING/BIOTECHNOLOGY 2017; 156:55-77. [PMID: 26907549 DOI: 10.1007/10_2015_5003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The increasing concerns of greenhouse gas emissions have increased the interest in dark fermentation as a means of productions for industrial chemicals, especially from renewable cellulosic biomass. However, the metabolism, including glycolysis, of many candidate organisms for cellulosic biomass conversion through consolidated bioprocessing is still poorly understood and the genomes have only recently been sequenced. Because a variety of industrial chemicals are produced directly from sugar metabolism, the careful understanding of glycolysis from a genomic and biochemical point of view is essential in the development of strategies for increasing product yields and therefore increasing industrial potential. The current review discusses the different pathways available for glycolysis along with unexpected variations from traditional models, especially in the utilization of alternate energy intermediates (GTP, pyrophosphate). This reinforces the need for a careful description of interactions between energy metabolites and glycolysis enzymes for understanding carbon and electron flux regulation.
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Affiliation(s)
- M Taillefer
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada, R3T 2N2
| | - R Sparling
- Department of Microbiology, University of Manitoba, Winnipeg, MB, Canada, R3T 2N2.
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39
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Biswas R, Wilson CM, Giannone RJ, Klingeman DM, Rydzak T, Shah MB, Hettich RL, Brown SD, Guss AM. Improved growth rate in Clostridium thermocellum hydrogenase mutant via perturbed sulfur metabolism. BIOTECHNOLOGY FOR BIOFUELS 2017; 10:6. [PMID: 28053665 PMCID: PMC5209896 DOI: 10.1186/s13068-016-0684-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Accepted: 12/08/2016] [Indexed: 05/16/2023]
Abstract
BACKGROUND Metabolic engineering is a commonly used approach to develop organisms for an industrial function, but engineering aimed at improving one phenotype can negatively impact other phenotypes. This lack of robustness can prove problematic. Cellulolytic bacterium Clostridium thermocellum is able to rapidly ferment cellulose to ethanol and other products. Recently, genes involved in H2 production, including the hydrogenase maturase hydG and NiFe hydrogenase ech, were deleted from the chromosome of C. thermocellum. While ethanol yield increased, the growth rate of ΔhydG decreased substantially compared to wild type. RESULTS Addition of 5 mM acetate to the growth medium improved the growth rate in C. thermocellum ∆hydG, whereas wild type remained unaffected. Transcriptomic analysis of the wild type showed essentially no response to the addition of acetate. However, in C. thermocellum ΔhydG, 204 and 56 genes were significantly differentially regulated relative to wild type in the absence and presence of acetate, respectively. Genes, Clo1313_0108-0125, which are predicted to encode a sulfate transport system and sulfate assimilatory pathway, were drastically upregulated in C. thermocellum ΔhydG in the presence of added acetate. A similar pattern was seen with proteomics. Further physiological characterization demonstrated an increase in sulfide synthesis and elimination of cysteine consumption in C. thermocellum ΔhydG. Clostridium thermocellum ΔhydGΔech had a higher growth rate than ΔhydG in the absence of added acetate, and a similar but less pronounced transcriptional and physiological effect was seen in this strain upon addition of acetate. CONCLUSIONS Sulfur metabolism is perturbed in C. thermocellum ΔhydG strains, likely to increase flux through sulfate reduction to act either as an electron sink to balance redox reactions or to offset an unknown deficiency in sulfur assimilation.
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Affiliation(s)
- Ranjita Biswas
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- Centre for Rural Development and Technology, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, 110016 India
| | - Charlotte M. Wilson
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Richard J. Giannone
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Dawn M. Klingeman
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Thomas Rydzak
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Manesh B. Shah
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Robert L. Hettich
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Steven D. Brown
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Adam M. Guss
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- One Bethel Valley Road, Oak Ridge, TN 37831-6038 USA
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40
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Atkinson JT, Campbell I, Bennett GN, Silberg JJ. Cellular Assays for Ferredoxins: A Strategy for Understanding Electron Flow through Protein Carriers That Link Metabolic Pathways. Biochemistry 2016; 55:7047-7064. [DOI: 10.1021/acs.biochem.6b00831] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Joshua T. Atkinson
- Systems,
Synthetic, and Physical Biology Graduate Program, Rice University, MS-180, 6100 Main Street, Houston, Texas 77005, United States
| | - Ian Campbell
- Biochemistry
and Cell Biology Graduate Program, Rice University, MS-140, 6100
Main Street, Houston, Texas 77005, United States
| | - George N. Bennett
- Department
of Biosciences, Rice University, MS-140, 6100 Main Street, Houston, Texas 77005, United States
- Department
of Chemical and Biomolecular Engineering, Rice University, MS-362,
6100 Main Street, Houston, Texas 77005, United States
| | - Jonathan J. Silberg
- Department
of Biosciences, Rice University, MS-140, 6100 Main Street, Houston, Texas 77005, United States
- Department
of Bioengineering, Rice University, MS-142, 6100 Main Street, Houston, Texas 77005, United States
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41
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Olson DG, Hörl M, Fuhrer T, Cui J, Zhou J, Maloney MI, Amador-Noguez D, Tian L, Sauer U, Lynd LR. Glycolysis without pyruvate kinase in Clostridium thermocellum. Metab Eng 2016; 39:169-180. [PMID: 27914869 DOI: 10.1016/j.ymben.2016.11.011] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 10/21/2016] [Accepted: 11/30/2016] [Indexed: 01/05/2023]
Abstract
The metabolism of Clostridium thermocellum is notable in that it assimilates sugar via the EMP pathway but does not possess a pyruvate kinase enzyme. In the wild type organism, there are three proposed pathways for conversion of phosphoenolpyruvate (PEP) to pyruvate, which differ in their cofactor usage. One path uses pyruvate phosphate dikinase (PPDK), another pathway uses the combined activities of PEP carboxykinase (PEPCK) and oxaloacetate decarboxylase (ODC). Yet another pathway, the malate shunt, uses the combined activities of PEPCK, malate dehydrogenase and malic enzyme. First we showed that there is no flux through the ODC pathway by enzyme assay. Flux through the remaining two pathways (PPDK and malate shunt) was determined by dynamic 13C labeling. In the wild-type strain, the malate shunt accounts for about 33±2% of the flux to pyruvate, with the remainder via the PPDK pathway. Deletion of the ppdk gene resulted in a redirection of all pyruvate flux through the malate shunt. This provides the first direct evidence of the in-vivo function of the malate shunt.
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Affiliation(s)
- Daniel G Olson
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
| | - Manuel Hörl
- Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
| | - Tobias Fuhrer
- Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
| | - Jingxuan Cui
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Jilai Zhou
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Marybeth I Maloney
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Daniel Amador-Noguez
- Department of Bacteriology, University of Wisconsin-Madison, Madison, WI 53706, USA
| | - Liang Tian
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Uwe Sauer
- Institute of Molecular Systems Biology, ETH Zurich, Zurich, Switzerland
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
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42
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Hon S, Lanahan AA, Tian L, Giannone RJ, Hettich RL, Olson DG, Lynd LR. Development of a plasmid-based expression system in Clostridium thermocellum and its use to screen heterologous expression of bifunctional alcohol dehydrogenases ( adhEs). Metab Eng Commun 2016; 3:120-129. [PMID: 29142822 PMCID: PMC5678826 DOI: 10.1016/j.meteno.2016.04.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 03/15/2016] [Accepted: 04/21/2016] [Indexed: 12/27/2022] Open
Abstract
Clostridium thermocellum is a promising candidate for ethanol production from cellulosic biomass, but requires metabolic engineering to improve ethanol yield. A key gene in the ethanol production pathway is the bifunctional aldehyde and alcohol dehydrogenase, adhE. To explore the effects of overexpressing wild-type, mutant, and exogenous adhEs, we developed a new expression plasmid, pDGO144, that exhibited improved transformation efficiency and better gene expression than its predecessor, pDGO-66. This new expression plasmid will allow for many other metabolic engineering and basic research efforts in C. thermocellum. As proof of concept, we used this plasmid to express 12 different adhE genes (both wild type and mutant) from several organisms. Ethanol production varied between clones immediately after transformation, but tended to converge to a single value after several rounds of serial transfer. The previously described mutant C. thermocellum D494G adhE gave the best ethanol production, which is consistent with previously published results.
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Affiliation(s)
- Shuen Hon
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
- BioEnergy Science Center, Oak Ridge, TN, USA
| | - Anthony A. Lanahan
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
- BioEnergy Science Center, Oak Ridge, TN, USA
| | - Liang Tian
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
- BioEnergy Science Center, Oak Ridge, TN, USA
| | - Richard J. Giannone
- BioEnergy Science Center, Oak Ridge, TN, USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Robert L. Hettich
- BioEnergy Science Center, Oak Ridge, TN, USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA
| | - Daniel G. Olson
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
- BioEnergy Science Center, Oak Ridge, TN, USA
| | - Lee R. Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, NH, USA
- BioEnergy Science Center, Oak Ridge, TN, USA
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43
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Advances in Consolidated Bioprocessing Using Clostridium thermocellumand Thermoanaerobacter saccharolyticum. Ind Biotechnol (New Rochelle N Y) 2016. [DOI: 10.1002/9783527807796.ch10] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
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44
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Ferredoxin:NAD+ Oxidoreductase of Thermoanaerobacterium saccharolyticum and Its Role in Ethanol Formation. Appl Environ Microbiol 2016; 82:7134-7141. [PMID: 27694237 DOI: 10.1128/aem.02130-16] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2016] [Accepted: 09/27/2016] [Indexed: 01/01/2023] Open
Abstract
Ferredoxin:NAD+ oxidoreductase (NADH-FNOR) catalyzes the transfer of electrons from reduced ferredoxin to NAD+ This enzyme has been hypothesized to be the main enzyme responsible for ferredoxin oxidization in the NADH-based ethanol pathway in Thermoanaerobacterium saccharolyticum; however, the corresponding gene has not yet been identified. Here, we identified the Tsac_1705 protein as a candidate FNOR based on the homology of its functional domains. We then confirmed its activity in vitro with a ferredoxin-based FNOR assay. To determine its role in metabolism, the tsac_1705 gene was deleted in different strains of T. saccharolyticum In wild-type T. saccharolyticum, deletion of tsac_1705 resulted in a 75% loss of NADH-FNOR activity, which indicated that Tsac_1705 is the main NADH-FNOR in T. saccharolyticum When both NADH- and NADPH-linked FNOR genes were deleted, the ethanol titer decreased and the ratio of ethanol to acetate approached unity, indicative of the absence of FNOR activity. Finally, we tested the effect of heterologous expression of Tsac_1705 in Clostridium thermocellum and found improvements in both the titer and the yield of ethanol. IMPORTANCE Redox balance plays a crucial role in many metabolic engineering strategies. Ferredoxins are widely used as electron carriers for anaerobic microorganism and plants. This study identified the gene responsible for electron transfer from ferredoxin to NAD+, a key reaction in the ethanol production pathway of this organism and many other metabolic pathways. Identification of this gene is an important step in transferring the ethanol production ability of this organism to other organisms.
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Lo J, Olson DG, Murphy SJL, Tian L, Hon S, Lanahan A, Guss AM, Lynd LR. Engineering electron metabolism to increase ethanol production in Clostridium thermocellum. Metab Eng 2016; 39:71-79. [PMID: 27989806 DOI: 10.1016/j.ymben.2016.10.018] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2016] [Revised: 10/17/2016] [Accepted: 10/25/2016] [Indexed: 11/28/2022]
Abstract
The NfnAB (NADH-dependent reduced ferredoxin: NADP+ oxidoreductase) and Rnf (ion-translocating reduced ferredoxin: NAD+ oxidoreductase) complexes are thought to catalyze electron transfer between reduced ferredoxin and NAD(P)+. Efficient electron flux is critical for engineering fuel production pathways, but little is known about the relative importance of these enzymes in vivo. In this study we investigate the importance of the NfnAB and Rnf complexes in Clostridium thermocellum for growth on cellobiose and Avicel using gene deletion, enzyme assays, and fermentation product analysis. The NfnAB complex does not seem to play a major role in metabolism, since deletion of nfnAB genes had little effect on the distribution of fermentation products. By contrast, the Rnf complex appears to play an important role in ethanol formation. Deletion of rnf genes resulted in a decrease in ethanol formation. Overexpression of rnf genes resulted in an increase in ethanol production of about 30%, but only in strains where the hydG hydrogenase maturation gene was also deleted.
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Affiliation(s)
- Jonathan Lo
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA
| | - Daniel G Olson
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA
| | - Sean Jean-Loup Murphy
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA
| | - Liang Tian
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA
| | - Shuen Hon
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA
| | - Anthony Lanahan
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA
| | - Adam M Guss
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Lee R Lynd
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
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CO2-fixing one-carbon metabolism in a cellulose-degrading bacterium Clostridium thermocellum. Proc Natl Acad Sci U S A 2016; 113:13180-13185. [PMID: 27794122 DOI: 10.1073/pnas.1605482113] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Clostridium thermocellum can ferment cellulosic biomass to formate and other end products, including CO2 This organism lacks formate dehydrogenase (Fdh), which catalyzes the reduction of CO2 to formate. However, feeding the bacterium 13C-bicarbonate and cellobiose followed by NMR analysis showed the production of 13C-formate in C. thermocellum culture, indicating the presence of an uncharacterized pathway capable of converting CO2 to formate. Combining genomic and experimental data, we demonstrated that the conversion of CO2 to formate serves as a CO2 entry point into the reductive one-carbon (C1) metabolism, and internalizes CO2 via two biochemical reactions: the reversed pyruvate:ferredoxin oxidoreductase (rPFOR), which incorporates CO2 using acetyl-CoA as a substrate and generates pyruvate, and pyruvate-formate lyase (PFL) converting pyruvate to formate and acetyl-CoA. We analyzed the labeling patterns of proteinogenic amino acids in individual deletions of all five putative PFOR mutants and in a PFL deletion mutant. We identified two enzymes acting as rPFOR, confirmed the dual activities of rPFOR and PFL crucial for CO2 uptake, and provided physical evidence of a distinct in vivo "rPFOR-PFL shunt" to reduce CO2 to formate while circumventing the lack of Fdh. Such a pathway precedes CO2 fixation via the reductive C1 metabolic pathway in C. thermocellum These findings demonstrated the metabolic versatility of C. thermocellum, which is thought of as primarily a cellulosic heterotroph but is shown here to be endowed with the ability to fix CO2 as well.
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Thompson RA, Dahal S, Garcia S, Nookaew I, Trinh CT. Exploring complex cellular phenotypes and model-guided strain design with a novel genome-scale metabolic model of Clostridium thermocellum DSM 1313 implementing an adjustable cellulosome. BIOTECHNOLOGY FOR BIOFUELS 2016; 9:194. [PMID: 27602057 PMCID: PMC5012057 DOI: 10.1186/s13068-016-0607-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Accepted: 08/26/2016] [Indexed: 05/06/2023]
Abstract
BACKGROUND Clostridium thermocellum is a gram-positive thermophile that can directly convert lignocellulosic material into biofuels. The metabolism of C. thermocellum contains many branches and redundancies which limit biofuel production, and typical genetic techniques are time-consuming. Further, the genome sequence of a genetically tractable strain C. thermocellum DSM 1313 has been recently sequenced and annotated. Therefore, developing a comprehensive, predictive, genome-scale metabolic model of DSM 1313 is desired for elucidating its complex phenotypes and facilitating model-guided metabolic engineering. RESULTS We constructed a genome-scale metabolic model iAT601 for DSM 1313 using the KEGG database as a scaffold and an extensive literature review and bioinformatic analysis for model refinement. Next, we used several sets of experimental data to train the model, e.g., estimation of the ATP requirement for growth-associated maintenance (13.5 mmol ATP/g DCW/h) and cellulosome synthesis (57 mmol ATP/g cellulosome/h). Using our tuned model, we investigated the effect of cellodextrin lengths on cell yields, and could predict in silico experimentally observed differences in cell yield based on which cellodextrin species is assimilated. We further employed our tuned model to analyze the experimentally observed differences in fermentation profiles (i.e., the ethanol to acetate ratio) between cellobiose- and cellulose-grown cultures and infer regulatory mechanisms to explain the phenotypic differences. Finally, we used the model to design over 250 genetic modification strategies with the potential to optimize ethanol production, 6155 for hydrogen production, and 28 for isobutanol production. CONCLUSIONS Our developed genome-scale model iAT601 is capable of accurately predicting complex cellular phenotypes under a variety of conditions and serves as a high-quality platform for model-guided strain design and metabolic engineering to produce industrial biofuels and chemicals of interest.
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Affiliation(s)
- R. Adam Thompson
- Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, TN 37996 USA
- Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Sanjeev Dahal
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- Comparative Genomics Group, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Sergio Garcia
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- Department of Chemical and Biomolecular Engineering, University of Tennessee, 1512 Middle Dr., DO#432, Knoxville, TN 37996 USA
| | - Intawat Nookaew
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- Comparative Genomics Group, Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- Department of Biomedical Informatics, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR 72205 USA
| | - Cong T. Trinh
- Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, TN 37996 USA
- Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- Department of Chemical and Biomolecular Engineering, University of Tennessee, 1512 Middle Dr., DO#432, Knoxville, TN 37996 USA
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Munir RI, Spicer V, Krokhin OV, Shamshurin D, Zhang X, Taillefer M, Blunt W, Cicek N, Sparling R, Levin DB. Transcriptomic and proteomic analyses of core metabolism in Clostridium termitidis CT1112 during growth on α-cellulose, xylan, cellobiose and xylose. BMC Microbiol 2016; 16:91. [PMID: 27215540 PMCID: PMC4877739 DOI: 10.1186/s12866-016-0711-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Accepted: 05/16/2016] [Indexed: 01/15/2023] Open
Abstract
Background Clostridium termitidis CT1112 is an anaerobic, Gram-positive, mesophilic, spore-forming, cellulolytic bacterium, originally isolated from the gut of a wood feeding termite Nasusitermes lujae. It has the ability to hydrolyze both cellulose and hemicellulose, and ferment the degradation products to acetate, formate, ethanol, lactate, H2, and CO2. It is therefore ges in gene and gene product expression during growth of C. termitidis on cellobiose, xylose, xylan, and α–cellulose. Results Correlation of transcriptome and proteome data with growth and fermentation profiles identified putative carbon-catabolism pathways in C. termitidis. The majority of the proteins associated with central metabolism were detected in high abundance. While major differences were not observed in gene and gene-product expression for enzymes associated with metabolic pathways under the different substrate conditions, xylulokinase and xylose isomerase of the pentose phosphate pathway were found to be highly up-regulated on five carbon sugars compared to hexoses. In addition, genes and gene-products associated with a variety of cellulosome and non-cellulosome associated CAZymes were found to be differentially expressed. Specifically, genes for cellulosomal enzymes and components were highly expressed on α–cellulose, while xylanases and glucosidases were up-regulated on 5 carbon sugars with respect to cellobiose. Chitinase and cellobiophosphorylases were the predominant CAZymes expressed on cellobiose. In addition to growth on xylan, the simultaneous consumption of two important lignocellulose constituents, cellobiose and xylose was also demonstrated. Conclusion There are little changes in core-metabolic pathways under the different carbon sources compared. The most significant differences were found to be associated with the CAZymes, as well as specific up regulation of some key components of the pentose phosphate pathway in the presence of xylose and xylan. This study has enhanced our understanding of the physiology and metabolism of C. termitidis, and provides a foundation for future studies on metabolic engineering to optimize biofuel production from natural biomass. Electronic supplementary material The online version of this article (doi:10.1186/s12866-016-0711-x) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Riffat I Munir
- Department of Biosystems Engineering, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Victor Spicer
- Department of Physics and Astronomy, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada.,Manitoba Centre for Proteomics and Systems Biology, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Oleg V Krokhin
- Manitoba Centre for Proteomics and Systems Biology, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Dmitry Shamshurin
- Manitoba Centre for Proteomics and Systems Biology, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - XiangLi Zhang
- Department of Plant Science, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Marcel Taillefer
- Department of Microbiology, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Warren Blunt
- Department of Biosystems Engineering, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Nazim Cicek
- Department of Biosystems Engineering, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - Richard Sparling
- Department of Microbiology, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada
| | - David B Levin
- Department of Biosystems Engineering, University of Manitoba, R3T 5N6, Winnipeg, MB, Canada.
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Abstract
Designer cellulosomes consist of chimeric cohesin-bearing scaffoldins for the controlled incorporation of recombinant dockerin-containing enzymes. The largest designer cellulosome reported to date is a chimeric scaffoldin that contains 6 cohesins. This scaffoldin represented a technical limit of sorts, since adding another cohesin proved problematic, owing to resultant low expression levels, instability (cleavage) of the scaffoldin polypeptide, and limited numbers of available cohesin-dockerin specificities—the hallmark of designer cellulosomes. Nevertheless, increasing the number of enzymes integrated into designer cellulosomes is critical, in order to further enhance degradation of plant cell wall material. Adaptor scaffoldins comprise an intermediate type of scaffoldin that can both incorporate various enzymes and attach to an additional scaffoldin. Using this strategy, we constructed an efficient form of adaptor scaffoldin that possesses three type I cohesins for enzyme integration, a single type II dockerin for interaction with an additional scaffoldin, and a carbohydrate-binding module for targeting to the cellulosic substrate. In parallel, we designed a hexavalent scaffoldin capable of connecting to the adaptor scaffoldin by the incorporation of an appropriate type II cohesin. The resultant extended designer cellulosome comprised 8 recombinant enzymes—4 xylanases and 4 cellulases—thereby representing a potent enzymatic cocktail for solubilization of natural lignocellulosic substrates. The contribution of the adaptor scaffoldin clearly demonstrated that proximity between the two scaffoldins and their composite set of enzymes is crucial for optimized degradation. After 72 h of incubation, the performance of the extended designer cellulosome was determined to be approximately 70% compared to that of native cellulosomes. Plant cell wall residues represent a major source of renewable biomass for the production of biofuels such as ethanol via breakdown to soluble sugars. The natural microbial degradation process, however, is inefficient for achieving cost-effective processes in the conversion of plant-derived biomass to biofuels, either from dedicated crops or human-generated cellulosic wastes. The accumulation of the latter is considered a major environmental pollutant. The development of designer cellulosome nanodevices for enhanced plant cell wall degradation thus has major impacts in the fields of environmental pollution, bioenergy production, and biotechnology in general. The findings reported in this article comprise a true breakthrough in our capacity to produce extended designer cellulosomes via synthetic biology means, thus enabling the assembly of higher-order complexes that can supersede the number of enzymes included in a single multienzyme complex.
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Sander K, Wilson CM, Rodriguez M, Klingeman DM, Rydzak T, Davison BH, Brown SD. Clostridium thermocellum DSM 1313 transcriptional responses to redox perturbation. BIOTECHNOLOGY FOR BIOFUELS 2015; 8:211. [PMID: 26692898 PMCID: PMC4676874 DOI: 10.1186/s13068-015-0394-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 11/24/2015] [Indexed: 05/21/2023]
Abstract
BACKGROUND Clostridium thermocellum is a promising consolidated bioprocessing candidate organism capable of directly converting lignocellulosic biomass to ethanol. Current ethanol yields, productivities, and growth inhibitions are industrial deployment impediments for commodity fuel production by this bacterium. Redox imbalance under certain conditions and in engineered strains may contribute to incomplete substrate utilization and may direct fermentation products to undesirable overflow metabolites. Towards a better understanding of redox metabolism in C. thermocellum, we established continuous growth conditions and analyzed global gene expression during addition of two stress chemicals (methyl viologen and hydrogen peroxide) which changed the fermentation redox potential. RESULTS The addition of methyl viologen to C. thermocellum DSM 1313 chemostat cultures caused an increase in ethanol and lactate yields. A lower fermenter redox potential was observed in response to methyl viologen exposure, which correlated with a decrease in cell yield and significant differential expression of 123 genes (log2 > 1.5 or log2 < -1.5, with a 5 % false discovery rate). Expression levels decreased in four main redox-active systems during methyl viologen exposure; the [NiFe] hydrogenase, sulfate transport and metabolism, ammonia assimilation (GS-GOGAT), and porphyrin/siroheme biosynthesis. Genes encoding sulfate transport and reduction and porphyrin/siroheme biosynthesis are co-located immediately downstream of a putative iscR regulatory gene, which may be a cis-regulatory element controlling expression of these genes. Other genes showing differential expression during methyl viologen exposure included transporters and transposases. CONCLUSIONS The differential expression results from this study support a role for C. thermocellum genes for sulfate transport/reduction, glutamate synthase-glutamine synthetase (the GS-GOGAT system), and porphyrin biosynthesis being involved in redox metabolism and homeostasis. This global profiling study provides gene targets for future studies to elucidate the relative contributions of prospective pathways for co-factor pool re-oxidation and C. thermocellum redox homeostasis.
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Affiliation(s)
- Kyle Sander
- />Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, TN 37996 USA
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN 37996 USA
| | - Charlotte M. Wilson
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Miguel Rodriguez
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Dawn M. Klingeman
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Thomas Rydzak
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Brian H. Davison
- />Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, TN 37996 USA
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Steven D. Brown
- />Bredesen Center for Interdisciplinary Research and Graduate Education, University of Tennessee, Knoxville, TN 37996 USA
- />BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
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