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Driessen JL, Johnsen J, Pogrebnyakov I, Mohamed ET, Mussatto SI, Feist AM, Jensen SI, Nielsen AT. Adaptive laboratory evolution of Bacillus subtilis to overcome toxicity of lignocellulosic hydrolysate derived from Distiller's dried grains with solubles (DDGS). Metab Eng Commun 2023; 16:e00223. [PMID: 37234932 PMCID: PMC10206485 DOI: 10.1016/j.mec.2023.e00223] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2023] [Revised: 04/03/2023] [Accepted: 04/26/2023] [Indexed: 05/28/2023] Open
Abstract
Microbial tolerance to toxic compounds formed during biomass pretreatment is a significant challenge to produce bio-based products from lignocellulose cost effectively. Rational engineering can be problematic due to insufficient prerequisite knowledge of tolerance mechanisms. Therefore, adaptive laboratory evolution was applied to obtain 20 tolerant lineages of Bacillus subtilis strains able to utilize Distiller's Dried Grains with Solubles-derived (DDGS) hydrolysate. Evolved strains showed both improved growth performance and retained heterologous enzyme production using 100% hydrolysate-based medium, whereas growth of the starting strains was essentially absent. Whole-genome resequencing revealed that evolved isolates acquired mutations in the global regulator codY in 15 of the 19 sequenced isolates. Furthermore, mutations in genes related to oxidative stress (katA, perR) and flagella function appeared in both tolerance and control evolution experiments without toxic compounds. Overall, tolerance adaptive laboratory evolution yielded strains able to utilize DDGS-hydrolysate to produce enzymes and hence proved to be a valuable tool for the valorization of lignocellulose.
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Affiliation(s)
- Jasper L.S.P. Driessen
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
| | - Josefin Johnsen
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
| | - Ivan Pogrebnyakov
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
| | - Elsayed T.T. Mohamed
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
| | - Solange I. Mussatto
- Department of Biotechnology and Biomedicine, Technical University of Denmark, Søltofts Plads 223, 2800, Kongens Lyngby, Denmark
| | - Adam M. Feist
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
- Department of Bioengineering, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA, 92093-0412, USA
| | - Sheila I. Jensen
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
| | - Alex T. Nielsen
- Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, Kemitorvet, 220, 2800, Kongens Lyngby, Denmark
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Yan C, Li X, Zhang G, Bi J, Hao H, Hou H. Quorum Sensing (QS)-regulated target predictions of Hafnia alvei H4 based on the joint application of genome and STRING database. Food Res Int 2022; 157:111356. [DOI: 10.1016/j.foodres.2022.111356] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Revised: 05/03/2022] [Accepted: 05/10/2022] [Indexed: 11/25/2022]
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Hebdon SD, Gerritsen AT, Chen YP, Marcano JG, Chou KJ. Genome-Wide Transcription Factor DNA Binding Sites and Gene Regulatory Networks in Clostridium thermocellum. Front Microbiol 2021; 12:695517. [PMID: 34566906 PMCID: PMC8457756 DOI: 10.3389/fmicb.2021.695517] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2021] [Accepted: 07/27/2021] [Indexed: 12/02/2022] Open
Abstract
Clostridium thermocellum is a thermophilic bacterium recognized for its natural ability to effectively deconstruct cellulosic biomass. While there is a large body of studies on the genetic engineering of this bacterium and its physiology to-date, there is limited knowledge in the transcriptional regulation in this organism and thermophilic bacteria in general. The study herein is the first report of a large-scale application of DNA-affinity purification sequencing (DAP-seq) to transcription factors (TFs) from a bacterium. We applied DAP-seq to > 90 TFs in C. thermocellum and detected genome-wide binding sites for 11 of them. We then compiled and aligned DNA binding sequences from these TFs to deduce the primary DNA-binding sequence motifs for each TF. These binding motifs are further validated with electrophoretic mobility shift assay (EMSA) and are used to identify individual TFs’ regulatory targets in C. thermocellum. Our results led to the discovery of novel, uncharacterized TFs as well as homologues of previously studied TFs including RexA-, LexA-, and LacI-type TFs. We then used these data to reconstruct gene regulatory networks for the 11 TFs individually, which resulted in a global network encompassing the TFs with some interconnections. As gene regulation governs and constrains how bacteria behave, our findings shed light on the roles of TFs delineated by their regulons, and potentially provides a means to enable rational, advanced genetic engineering of C. thermocellum and other organisms alike toward a desired phenotype.
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Affiliation(s)
- Skyler D Hebdon
- Biosciences Center, National Renewable Energy Laboratory, Golden, CO, United States
| | - Alida T Gerritsen
- Computational Sciences Center, National Renewable Energy Laboratory, Golden, CO, United States
| | - Yi-Pei Chen
- Biosciences Center, National Renewable Energy Laboratory, Golden, CO, United States
| | - Joan G Marcano
- Biosciences Center, National Renewable Energy Laboratory, Golden, CO, United States
| | - Katherine J Chou
- Biosciences Center, National Renewable Energy Laboratory, Golden, CO, United States
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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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Ha-Tran DM, Lai RY, Nguyen TTM, Huang E, Lo SC, Huang CC. Construction of engineered RuBisCO Kluyveromyces marxianus for a dual microbial bioethanol production system. PLoS One 2021; 16:e0247135. [PMID: 33661900 PMCID: PMC7932148 DOI: 10.1371/journal.pone.0247135] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2020] [Accepted: 02/02/2021] [Indexed: 11/28/2022] Open
Abstract
Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) genes play important roles in CO2 fixation and redox balancing in photosynthetic bacteria. In the present study, the kefir yeast Kluyveromyces marxianus 4G5 was used as host for the transformation of form I and form II RubisCO genes derived from the nonsulfur purple bacterium Rhodopseudomonas palustris using the Promoter-based Gene Assembly and Simultaneous Overexpression (PGASO) method. Hungateiclostridium thermocellum ATCC 27405, a well-known bacterium for its efficient solubilization of recalcitrant lignocellulosic biomass, was used to degrade Napier grass and rice straw to generate soluble fermentable sugars. The resultant Napier grass and rice straw broths were used as growth media for the engineered K. marxianus. In the dual microbial system, H. thermocellum degraded the biomass feedstock to produce both C5 and C6 sugars. As the bacterium only used hexose sugars, the remaining pentose sugars could be metabolized by K. marxianus to produce ethanol. The transformant RubisCO K. marxianus strains grew well in hydrolyzed Napier grass and rice straw broths and produced bioethanol more efficiently than the wild type. Therefore, these engineered K. marxianus strains could be used with H. thermocellum in a bacterium-yeast coculture system for ethanol production directly from biomass feedstocks.
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Affiliation(s)
- Dung Minh Ha-Tran
- Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program, Academia Sinica and National Chung Hsing University, Taipei, Taiwan
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
- Graduate Institute of Biotechnology, National Chung Hsing University, Taichung, Taiwan
| | - Rou-Yin Lai
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
| | - Trinh Thi My Nguyen
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
| | - Eugene Huang
- College of Agriculture and Natural Resources, National Chung Hsing University, Taichung, Taiwan
| | - Shou-Chen Lo
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
- * E-mail: (SCL); (CCH)
| | - Chieh-Chen Huang
- Department of Life Sciences, National Chung Hsing University, Taichung, Taiwan
- Innovation and Development Center of Sustainable Agriculture, National Chung Hsing University, Taichung, Taiwan
- * E-mail: (SCL); (CCH)
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Sander KB, Chung D, Klingeman DM, Giannone RJ, Rodriguez M, Whitham J, Hettich RL, Davison BH, Westpheling J, Brown SD. Gene targets for engineering osmotolerance in Caldicellulosiruptor bescii. BIOTECHNOLOGY FOR BIOFUELS 2020; 13:50. [PMID: 32190115 PMCID: PMC7071700 DOI: 10.1186/s13068-020-01690-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2019] [Accepted: 02/27/2020] [Indexed: 05/05/2023]
Abstract
BACKGROUND Caldicellulosiruptor bescii, a promising biocatalyst being developed for use in consolidated bioprocessing of lignocellulosic materials to ethanol, grows poorly and has reduced conversion at elevated medium osmolarities. Increasing tolerance to elevated fermentation osmolarities is desired to enable performance necessary of a consolidated bioprocessing (CBP) biocatalyst. RESULTS Two strains of C. bescii showing growth phenotypes in elevated osmolarity conditions were identified. The first strain, ORCB001, carried a deletion of the FapR fatty acid biosynthesis and malonyl-CoA metabolism repressor and had a severe growth defect when grown in high-osmolarity conditions-introduced as the addition of either ethanol, NaCl, glycerol, or glucose to growth media. The second strain, ORCB002, displayed a growth rate over three times higher than its genetic parent when grown in high-osmolarity medium. Unexpectedly, a genetic complement ORCB002 exhibited improved growth, failing to revert the observed phenotype, and suggesting that mutations other than the deleted transcription factor (the fruR/cra gene) are responsible for the growth phenotype observed in ORCB002. Genome resequencing identified several other genomic alterations (three deleted regions, three substitution mutations, one silent mutation, and one frameshift mutation), which may be responsible for the observed increase in osmolarity tolerance in the fruR/cra-deficient strain, including a substitution mutation in dnaK, a gene previously implicated in osmoresistance in bacteria. Differential expression analysis and transcription factor binding site inference indicates that FapR negatively regulates malonyl-CoA and fatty acid biosynthesis, as it does in many other bacteria. FruR/Cra regulates neighboring fructose metabolism genes, as well as other genes in global manner. CONCLUSIONS Two systems able to effect tolerance to elevated osmolarities in C. bescii are identified. The first is fatty acid biosynthesis. The other is likely the result of one or more unintended, secondary mutations present in another transcription factor deletion strain. Though the locus/loci and mechanism(s) responsible remain unknown, candidate mutations are identified, including a mutation in the dnaK chaperone coding sequence. These results illustrate both the promise of targeted regulatory manipulation for osmotolerance (in the case of fapR) and the challenges (in the case of fruR/cra).
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Affiliation(s)
- Kyle B. Sander
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Bredesen Center for Interdisciplinary Graduate Research and Education, University of Tennessee, Knoxville, TN USA
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN USA
- Present Address: Department of Bioengineering, University of California, Berkeley, Berkeley, CA USA
| | - Daehwan Chung
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Department of Genetics, University of Georgia, Athens, GA USA
- Present Address: National Bioenergy Center, National Renewable Energy Laboratory, Golden, CO USA
| | - Dawn M. Klingeman
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Richard J. Giannone
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Miguel Rodriguez
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Jason Whitham
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Present Address: Becton Dickinson Diagnostics, Sparks Glencoe, MD USA
| | - Robert L. Hettich
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Brian H. Davison
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Bredesen Center for Interdisciplinary Graduate Research and Education, University of Tennessee, Knoxville, TN USA
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Janet Westpheling
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Department of Genetics, University of Georgia, Athens, GA USA
| | - Steven D. Brown
- BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Bredesen Center for Interdisciplinary Graduate Research and Education, University of Tennessee, Knoxville, TN USA
- Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN USA
- Present Address: LanzaTech, Skokie, IL USA
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Banerjee S, Mishra G, Roy A. Metabolic Engineering of Bacteria for Renewable Bioethanol Production from Cellulosic Biomass. BIOTECHNOL BIOPROC E 2019. [DOI: 10.1007/s12257-019-0134-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Sandberg TE, Salazar MJ, Weng LL, Palsson BO, Feist AM. The emergence of adaptive laboratory evolution as an efficient tool for biological discovery and industrial biotechnology. Metab Eng 2019; 56:1-16. [PMID: 31401242 DOI: 10.1016/j.ymben.2019.08.004] [Citation(s) in RCA: 251] [Impact Index Per Article: 50.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2019] [Revised: 08/01/2019] [Accepted: 08/05/2019] [Indexed: 12/21/2022]
Abstract
Harnessing the process of natural selection to obtain and understand new microbial phenotypes has become increasingly possible due to advances in culturing techniques, DNA sequencing, bioinformatics, and genetic engineering. Accordingly, Adaptive Laboratory Evolution (ALE) experiments represent a powerful approach both to investigate the evolutionary forces influencing strain phenotypes, performance, and stability, and to acquire production strains that contain beneficial mutations. In this review, we summarize and categorize the applications of ALE to various aspects of microbial physiology pertinent to industrial bioproduction by collecting case studies that highlight the multitude of ways in which evolution can facilitate the strain construction process. Further, we discuss principles that inform experimental design, complementary approaches such as computational modeling that help maximize utility, and the future of ALE as an efficient strain design and build tool driven by growing adoption and improvements in automation.
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Affiliation(s)
- Troy E Sandberg
- Department of Bioengineering, University of California, San Diego, CA, 92093, USA
| | - Michael J Salazar
- Department of Bioengineering, University of California, San Diego, CA, 92093, USA
| | - Liam L Weng
- Department of Bioengineering, University of California, San Diego, CA, 92093, USA
| | - Bernhard O Palsson
- Department of Bioengineering, University of California, San Diego, CA, 92093, USA; Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800, Lyngby, Denmark
| | - Adam M Feist
- Department of Bioengineering, University of California, San Diego, CA, 92093, USA; Novo Nordisk Foundation Center for Biosustainability, Technical University of Denmark, 2800, Lyngby, Denmark.
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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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Poudel S, Giannone RJ, Rodriguez M, Raman B, Martin MZ, Engle NL, Mielenz JR, Nookaew I, Brown SD, Tschaplinski TJ, Ussery D, Hettich RL. Integrated omics analyses reveal the details of metabolic adaptation of Clostridium thermocellum to lignocellulose-derived growth inhibitors released during the deconstruction of switchgrass. BIOTECHNOLOGY FOR BIOFUELS 2017; 10:14. [PMID: 28077967 PMCID: PMC5223564 DOI: 10.1186/s13068-016-0697-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2016] [Accepted: 12/24/2016] [Indexed: 05/03/2023]
Abstract
BACKGROUND Clostridium thermocellum is capable of solubilizing and converting lignocellulosic biomass into ethanol. Although much of the work-to-date has centered on characterizing this microbe's growth on model cellulosic substrates, such as cellobiose, Avicel, or filter paper, it is vitally important to understand its metabolism on more complex, lignocellulosic substrates to identify relevant industrial bottlenecks that could undermine efficient biofuel production. To this end, we have examined a time course progression of C. thermocellum grown on switchgrass to assess the metabolic and protein changes that occur during the conversion of plant biomass to ethanol. RESULTS The most striking feature of the metabolome was the observed accumulation of long-chain, branched fatty acids over time, implying an adaptive restructuring of C. thermocellum's cellular membrane as the culture progresses. This is undoubtedly a response to the gradual accumulation of lignocellulose-derived inhibitory compounds as the organism deconstructs the switchgrass to access the embedded cellulose. Corroborating the metabolomics data, proteomic analysis revealed a corresponding time-dependent increase in various enzymes, including those involved in the interconversion of branched amino acids valine, leucine, and isoleucine to iso- and anteiso-fatty acid precursors. Additionally, the metabolic accumulation of hemicellulose-derived sugars and sugar alcohols concomitant with increased abundance of enzymes involved in C5 sugar metabolism/pentose phosphate pathway indicates that C. thermocellum shifts glycolytic intermediates to alternate pathways to modulate overall carbon flux in response to C5 sugar metabolites that increase during lignocellulose deconstruction. CONCLUSIONS Integrated omic platforms provided complementary systems biological information that highlight C. thermocellum's specific response to cytotoxic inhibitors released during the deconstruction and utilization of switchgrass. These additional viewpoints allowed us to fully realize the level to which the organism adapts to an increasingly challenging culture environment-information that will prove critical to C. thermocellum's industrial efficacy.
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Affiliation(s)
- Suresh Poudel
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
- Department of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996 USA
| | | | - Miguel Rodriguez
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
| | - Babu Raman
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
- Dow AgroSciences, 9330 Zionsville Road, Indianapolis, IN 46268 USA
| | - Madhavi Z. Martin
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
| | - Nancy L. Engle
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
| | | | - Intawat Nookaew
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
- Department of Biomedical Informatics, University of Arkansas for Medical Sciences, Little Rock, AR 72205 USA
| | - Steven D. Brown
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
- Department of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996 USA
| | | | - David Ussery
- Biosciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
- Department of Biomedical Informatics, University of Arkansas for Medical Sciences, Little Rock, AR 72205 USA
| | - Robert L. Hettich
- Chemical Sciences Division, Oak Ridge National Lab, Oak Ridge, TN 37831 USA
- Department of Genome Science and Technology, University of Tennessee, Knoxville, TN 37996 USA
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Ábrego U, Chen Z, Wan C. Consolidated Bioprocessing Systems for Cellulosic Biofuel Production. ADVANCES IN BIOENERGY 2017. [DOI: 10.1016/bs.aibe.2017.01.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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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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13
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Tian L, Papanek B, Olson DG, Rydzak T, Holwerda EK, Zheng T, Zhou J, Maloney M, Jiang N, Giannone RJ, Hettich RL, Guss AM, Lynd LR. Simultaneous achievement of high ethanol yield and titer in Clostridium thermocellum. BIOTECHNOLOGY FOR BIOFUELS 2016; 9:116. [PMID: 27257435 PMCID: PMC4890492 DOI: 10.1186/s13068-016-0528-8] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Accepted: 05/19/2016] [Indexed: 05/03/2023]
Abstract
BACKGROUND Biofuel production from plant cell walls offers the potential for sustainable and economically attractive alternatives to petroleum-based products. Fuels from cellulosic biomass are particularly promising, but would benefit from lower processing costs. Clostridium thermocellum can rapidly solubilize and ferment cellulosic biomass, making it a promising candidate microorganism for consolidated bioprocessing for biofuel production, but increases in product yield and titer are still needed. RESULTS Here, we started with an engineered C. thermocellum strain where the central metabolic pathways to products other than ethanol had been deleted. After two stages of adaptive evolution, an evolved strain was selected with improved yield and titer. On chemically defined medium with crystalline cellulose as substrate, the evolved strain produced 22.4 ± 1.4 g/L ethanol from 60 g/L cellulose. The resulting yield was about 0.39 gETOH/gGluc eq, which is 75 % of the maximum theoretical yield. Genome resequencing, proteomics, and biochemical analysis were used to examine differences between the original and evolved strains. CONCLUSIONS A two step selection method successfully improved the ethanol yield and the titer. This evolved strain has the highest ethanol yield and titer reported to date for C. thermocellum, and is an important step in the development of this microbe for industrial applications.
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Affiliation(s)
- Liang Tian
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Beth Papanek
- />Bredesen Center, University of Tennessee, Knoxville, TN 37996 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Daniel G. Olson
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Thomas Rydzak
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Evert K. Holwerda
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Tianyong Zheng
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Jilai Zhou
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Marybeth Maloney
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Nannan Jiang
- />Bredesen Center, University of Tennessee, Knoxville, TN 37996 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Bioenergy Science Center, 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
| | - 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
| | - Adam M. Guss
- />Bredesen Center, University of Tennessee, Knoxville, TN 37996 USA
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Lee R. Lynd
- />Thayer School of Engineering, Dartmouth College, 14 Engineering Drive, Hanover, NH 03755 USA
- />Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
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Dumitrache A, Akinosho H, Rodriguez M, Meng X, Yoo CG, Natzke J, Engle NL, Sykes RW, Tschaplinski TJ, Muchero W, Ragauskas AJ, Davison BH, Brown SD. Consolidated bioprocessing of Populus using Clostridium (Ruminiclostridium) thermocellum: a case study on the impact of lignin composition and structure. BIOTECHNOLOGY FOR BIOFUELS 2016; 9:31. [PMID: 26855670 PMCID: PMC4743434 DOI: 10.1186/s13068-016-0445-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Accepted: 01/20/2016] [Indexed: 05/04/2023]
Abstract
BACKGROUND Higher ratios of syringyl-to-guaiacyl (S/G) lignin components of Populus were shown to improve sugar release by enzymatic hydrolysis using commercial blends. Cellulolytic microbes are often robust biomass hydrolyzers and may offer cost advantages; however, it is unknown whether their activity can also be significantly influenced by the ratio of different monolignol types in Populus biomass. Hydrolysis and fermentation of autoclaved, but otherwise not pretreated Populus trichocarpa by Clostridium thermocellum ATCC 27405 was compared using feedstocks that had similar carbohydrate and total lignin contents but differed in S/G ratios. RESULTS Populus with an S/G ratio of 2.1 was converted more rapidly and to a greater extent compared to similar biomass that had a ratio of 1.2. For either microbes or commercial enzymes, an approximate 50 % relative difference in total solids solubilization was measured for both biomasses, which suggests that the differences and limitations in the microbial breakdown of lignocellulose may be largely from the enzymatic hydrolytic process. Surprisingly, the reduction in glucan content per gram solid in the residual microbially processed biomass was similar (17-18 %) irrespective of S/G ratio, pointing to a similar mechanism of solubilization that proceeded at different rates. Fermentation metabolome testing did not reveal the release of known biomass-derived alcohol and aldehyde inhibitors that could explain observed differences in microbial hydrolytic activity. Biomass-derived p-hydroxybenzoic acid was up to nine-fold higher in low S/G ratio biomass fermentations, but was not found to be inhibitory in subsequent test fermentations. Cellulose crystallinity and degree of polymerization did not vary between Populus lines and had minor changes after fermentation. However, lignin molecular weights and cellulose accessibility determined by Simons' staining were positively correlated to the S/G content. CONCLUSIONS Higher S/G ratios in Populus biomass lead to longer and more linear lignin chains and greater access to surface cellulosic content by microbe-bound enzymatic complexes. Substrate access limitation is suggested as a primary bottleneck in solubilization of minimally processed Populus, which has important implications for microbial deconstruction of lignocellulose biomass. Our findings will allow others to examine different Populus lines and to test if similar observations are possible for other plant species.
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Affiliation(s)
- Alexandru Dumitrache
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Hannah Akinosho
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- />Renewable Bioproducts Institute, Georgia Institute of Technology, Atlanta, GA 30332 USA
- />UT-ORNL Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Miguel Rodriguez
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Xianzhi Meng
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- />Renewable Bioproducts Institute, Georgia Institute of Technology, Atlanta, GA 30332 USA
- />School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, GA 30332 USA
| | - Chang Geun Yoo
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- />UT-ORNL Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
| | - Jace Natzke
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Nancy L. Engle
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Robert W. Sykes
- />National Renewable Energy Laboratory, US Department of Energy, Golden, CO 80401 USA
| | - Timothy J. Tschaplinski
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Wellington Muchero
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Arthur J. Ragauskas
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
- />UT-ORNL Joint Institute for Biological Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />Department of Chemical and Biomolecular Engineering, Department of Forestry, Wildlife, and Fisheries, University of Tennessee, Knoxville, TN 37996 USA
| | - Brian H. Davison
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
| | - Steven D. Brown
- />Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA
- />BioEnergy Sciences Center, Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830 USA
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Akinosho H, Rydzak T, Borole A, Ragauskas A, Close D. Toxicological challenges to microbial bioethanol production and strategies for improved tolerance. ECOTOXICOLOGY (LONDON, ENGLAND) 2015; 24:2156-2174. [PMID: 26423392 DOI: 10.1007/s10646-015-1543-4] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Accepted: 09/16/2015] [Indexed: 06/05/2023]
Abstract
Bioethanol production output has increased steadily over the last two decades and is now beginning to become competitive with traditional liquid transportation fuels due to advances in engineering, the identification of new production host organisms, and the development of novel biodesign strategies. A significant portion of these efforts has been dedicated to mitigating the toxicological challenges encountered across the bioethanol production process. From the release of potentially cytotoxic or inhibitory compounds from input feedstocks, through the metabolic co-synthesis of ethanol and potentially detrimental byproducts, and to the potential cytotoxicity of ethanol itself, each stage of bioethanol production requires the application of genetic or engineering controls that ensure the host organisms remain healthy and productive to meet the necessary economies required for large scale production. In addition, as production levels continue to increase, there is an escalating focus on the detoxification of the resulting waste streams to minimize their environmental impact. This review will present the major toxicological challenges encountered throughout each stage of the bioethanol production process and the commonly employed strategies for reducing or eliminating potential toxic effects.
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Affiliation(s)
- Hannah Akinosho
- Renewable BioProducts Institute, Georgia Institute of Technology, Atlanta, GA, USA
- BioEnergy Science Center, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831, USA
| | - Thomas Rydzak
- BioEnergy Science Center, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831, USA
- Biosciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS6342, Oak Ridge, TN, 37831-6342, USA
| | - Abhijeet Borole
- Biosciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS6342, Oak Ridge, TN, 37831-6342, USA
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, USA
- Bredesen Center for Interdisciplinary Research and Education, University of Tennessee, Knoxville, TN, USA
| | - Arthur Ragauskas
- Renewable BioProducts Institute, Georgia Institute of Technology, Atlanta, GA, USA
- BioEnergy Science Center, Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN, 37831, USA
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, USA
| | - Dan Close
- Biosciences Division, Oak Ridge National Laboratory, P.O. Box 2008, MS6342, Oak Ridge, TN, 37831-6342, USA.
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Elimination of metabolic pathways to all traditional fermentation products increases ethanol yields in Clostridium thermocellum. Metab Eng 2015; 32:49-54. [PMID: 26369438 DOI: 10.1016/j.ymben.2015.09.002] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2015] [Revised: 08/27/2015] [Accepted: 09/02/2015] [Indexed: 01/01/2023]
Abstract
Clostridium thermocellum has the natural ability to convert cellulose to ethanol, making it a promising candidate for consolidated bioprocessing (CBP) of cellulosic biomass to biofuels. To further improve its CBP capabilities, a mutant strain of C. thermocellum was constructed (strain AG553; C. thermocellum Δhpt ΔhydG Δldh Δpfl Δpta-ack) to increase flux to ethanol by removing side product formation. Strain AG553 showed a two- to threefold increase in ethanol yield relative to the wild type on all substrates tested. On defined medium, strain AG553 exceeded 70% of theoretical ethanol yield on lower loadings of the model crystalline cellulose Avicel, effectively eliminating formate, acetate, and lactate production and reducing H2 production by fivefold. On 5 g/L Avicel, strain AG553 reached an ethanol yield of 63.5% of the theoretical maximum compared with 19.9% by the wild type, and it showed similar yields on pretreated switchgrass and poplar. The elimination of organic acid production suggested that the strain might be capable of growth under higher substrate loadings in the absence of pH control. Final ethanol titer peaked at 73.4mM in mutant AG553 on 20 g/L Avicel, at which point the pH decreased to a level that does not allow growth of C. thermocellum, likely due to CO2 accumulation. In comparison, the maximum titer of wild type C. thermocellum was 14.1mM ethanol on 10 g/L Avicel. With the elimination of the metabolic pathways to all traditional fermentation products other than ethanol, AG553 is the best ethanol-yielding CBP strain to date and will serve as a platform strain for further metabolic engineering for the bioconversion of lignocellulosic biomass.
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Development of a regulatable plasmid-based gene expression system for Clostridium thermocellum. Appl Microbiol Biotechnol 2015; 99:7589-99. [DOI: 10.1007/s00253-015-6610-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 04/07/2015] [Accepted: 04/15/2015] [Indexed: 01/31/2023]
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Tools for developing tolerance to toxic chemicals in microbial systems and perspectives on moving the field forward and into the industrial setting. Curr Opin Chem Eng 2014. [DOI: 10.1016/j.coche.2014.08.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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Akinosho H, Yee K, Close D, Ragauskas A. The emergence of Clostridium thermocellum as a high utility candidate for consolidated bioprocessing applications. Front Chem 2014; 2:66. [PMID: 25207268 PMCID: PMC4143619 DOI: 10.3389/fchem.2014.00066] [Citation(s) in RCA: 105] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2014] [Accepted: 07/28/2014] [Indexed: 01/25/2023] Open
Abstract
First isolated in 1926, Clostridium thermocellum has recently received increased attention as a high utility candidate for use in consolidated bioprocessing (CBP) applications. These applications, which seek to process lignocellulosic biomass directly into useful products such as ethanol, are gaining traction as economically feasible routes toward the production of fuel and other high value chemical compounds as the shortcomings of fossil fuels become evident. This review evaluates C. thermocellum's role in this transitory process by highlighting recent discoveries relating to its genomic, transcriptomic, proteomic, and metabolomic responses to varying biomass sources, with a special emphasis placed on providing an overview of its unique, multivariate enzyme cellulosome complex and the role that this structure performs during biomass degradation. Both naturally evolved and genetically engineered strains are examined in light of their unique attributes and responses to various biomass treatment conditions, and the genetic tools that have been employed for their creation are presented. Several future routes for potential industrial usage are presented, and it is concluded that, although there have been many advances to significantly improve C. thermocellum's amenability to industrial use, several hurdles still remain to be overcome as this unique organism enjoys increased attention within the scientific community.
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Affiliation(s)
- Hannah Akinosho
- School of Chemistry and Biochemistry, Institute of Paper Science and Technology, Georgia Institute of Technology Atlanta, GA, USA ; Oak Ridge National Laboratory, BioEnergy Science Center Oak Ridge, TN, USA
| | - Kelsey Yee
- Oak Ridge National Laboratory, BioEnergy Science Center Oak Ridge, TN, USA ; Biosciences Division, Oak Ridge National Laboratory Oak Ridge, TN, USA
| | - Dan Close
- Biosciences Division, Oak Ridge National Laboratory Oak Ridge, TN, USA
| | - Arthur Ragauskas
- Oak Ridge National Laboratory, BioEnergy Science Center Oak Ridge, TN, USA ; Department of Chemical and Biomolecular Engineering and Department of Forestry, Wildlife, and Fisheries, University of Tennessee Knoxville, TN, USA
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Linville JL, Rodriguez M, Brown SD, Mielenz JR, Cox CD. Transcriptomic analysis of Clostridium thermocellum Populus hydrolysate-tolerant mutant strain shows increased cellular efficiency in response to Populus hydrolysate compared to the wild type strain. BMC Microbiol 2014; 14:215. [PMID: 25128475 PMCID: PMC4236516 DOI: 10.1186/s12866-014-0215-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2013] [Accepted: 08/08/2014] [Indexed: 12/19/2022] Open
Abstract
Background The thermophilic, anaerobic bacterium, Clostridium thermocellum is a model organism for consolidated processing due to its efficient fermentation of cellulose. Constituents of dilute acid pretreatment hydrolysate are known to inhibit C. thermocellum and other microorganisms. To evaluate the biological impact of this type of hydrolysate, a transcriptomic analysis of growth in hydrolysate-containing medium was conducted on 17.5% v/v Populus hydrolysate-tolerant mutant (PM) and wild type (WT) strains of C. thermocellum. Results In two levels of Populus hydrolysate medium (0% and 10% v/v), the PM showed both gene specific increases and decreases of gene expression compared to the wild-type strain. The PM had increased expression of genes in energy production and conversion, and amino acid transport and metabolism in both standard and 10% v/v Populus hydrolysate media. In particular, expression of the histidine metabolism increased up to 100 fold. In contrast, the PM decreased gene expression in cell division and sporulation (standard medium only), cell defense mechanisms, cell envelope, cell motility, and cellulosome in both media. The PM downregulated inorganic ion transport and metabolism in standard medium but upregulated it in the hydrolysate media when compared to the WT. The WT differentially expressed 1072 genes in response to the hydrolysate medium which included increased transcription of cell defense mechanisms, cell motility, and cellulosome, and decreased expression in cell envelope, amino acid transport and metabolism, inorganic ion transport and metabolism, and lipid metabolism, while the PM only differentially expressed 92 genes. The PM tolerates up to 17.5% v/v Populus hydrolysate and growth in it elicited 489 genes with differential expression, which included increased expression in energy production and conversion, cellulosome production, and inorganic ion transport and metabolism and decreased expression in transcription and cell defense mechanisms. Conclusion These results suggest the mechanisms of tolerance for the Populus hydrolysate-tolerant mutant strain of C. thermocellum are based on increased cellular efficiency caused apparently by downregulation of non-critical genes and increasing the expression of genes in energy production and conversion rather than tolerance to specific hydrolysate components. The wild type, conversely, responds to hydrolysate media by down-regulating growth genes and up-regulating stress response genes.
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Affiliation(s)
| | | | | | | | - Chris D Cox
- Department of Civil and Environmental Engineering, University of Tennessee, Knoxville, TN, USA.
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