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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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Gong C, Cao L, Fang D, Zhang J, Kumar Awasthi M, Xue D. Genetic manipulation strategies for ethanol production from bioconversion of lignocellulose waste. BIORESOURCE TECHNOLOGY 2022; 352:127105. [PMID: 35378286 DOI: 10.1016/j.biortech.2022.127105] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 03/28/2022] [Accepted: 03/30/2022] [Indexed: 06/14/2023]
Abstract
Lignocellulose waste was served as promising raw material for bioethanol production. Bioethanol was considered to be a potential alternative energy to take the place of fossil fuels. Lignocellulosic biomass synthesized by plants is regenerative, sufficient and cheap source for bioethanol production. The biotransformation of lignocellulose could exhibit dual significance-reduction of pollution and obtaining of energy. Some strategies are being developing and increasing the utilization of lignocellulose waste to produce ethanol. New technology of bioethanol production from natural lignocellulosic biomass is required. In this paper, the progress in genetic manipulation strategies including gene editing and synthetic genomics for the transformation from lignocellulose to ethanol was reviewed. At last, the application prospect of bioethanol was introduced.
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Affiliation(s)
- Chunjie Gong
- Key Laboratory of Fermentation Engineering (Ministry of Education), National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan 430068, PR China
| | - Liping Cao
- Key Laboratory of Fermentation Engineering (Ministry of Education), National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan 430068, PR China
| | - Donglai Fang
- Key Laboratory of Fermentation Engineering (Ministry of Education), National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan 430068, PR China
| | - Jiaqi Zhang
- Key Laboratory of Fermentation Engineering (Ministry of Education), National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan 430068, PR China
| | - Mukesh Kumar Awasthi
- College of Natural Resources and Environment, Northwest A&F University, Yangling, Shaanxi 712100, PR China
| | - Dongsheng Xue
- Key Laboratory of Fermentation Engineering (Ministry of Education), National "111" Center for Cellular Regulation and Molecular Pharmaceutics, Hubei University of Technology, Wuhan 430068, PR China.
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Le Y, Sun J. CRISPR/Cas genome editing systems in thermophiles: Current status, associated challenges, and future perspectives. ADVANCES IN APPLIED MICROBIOLOGY 2022; 118:1-30. [PMID: 35461662 DOI: 10.1016/bs.aambs.2022.02.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Thermophiles, offering an attractive and unique platform for a broad range of applications in biofuels and environment protections, have received a significant attention and growing interest from academy and industry. However, the exploration and exploitation of thermophilic organisms have been hampered by the lack of a powerful genome manipulation tool to improve production efficiency. At current, the clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/CRISPR associated (Cas) system has been successfully exploited as a competent, simplistic, and powerful tool for genome engineering both in eukaryotes and prokaryotes. Indeed, with the significant efforts made in recent years, some thermostable Cas9 proteins have been well identified and characterized and further, some thermostable Cas9-based editing tools have been successfully established in some representative obligate thermophiles. In this regard, we reviewed the current status and its progress in CRISPR/Cas-based genome editing system towards a variety of thermophilic organisms. Despite the potentials of these progresses, multiple factors/barriers still have to be overcome and optimized for improving its editing efficiency in thermophiles. Some insights into the roles of thermostable CRISPR/Cas technologies for the metabolic engineering of thermophiles as a thermophilic microbial cell factory were also fully analyzed and discussed.
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Affiliation(s)
- Yilin Le
- Biofuels institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, Jiangsu, PR China.
| | - Jianzhong Sun
- Biofuels institute, School of the Environment and Safety Engineering, Jiangsu University, Zhenjiang, Jiangsu, PR China.
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Assessing the impact of substrate-level enzyme regulations limiting ethanol titer in Clostridium thermocellum using a core kinetic model. Metab Eng 2022; 69:286-301. [PMID: 34982997 DOI: 10.1016/j.ymben.2021.12.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 12/16/2021] [Accepted: 12/29/2021] [Indexed: 11/20/2022]
Abstract
Clostridium thermocellum is a promising candidate for consolidated bioprocessing because it can directly ferment cellulose to ethanol. Despite significant efforts, achieved yields and titers fall below industrially relevant targets. This implies that there still exist unknown enzymatic, regulatory, and/or possibly thermodynamic bottlenecks that can throttle back metabolic flow. By (i) elucidating internal metabolic fluxes in wild-type C. thermocellum grown on cellobiose via 13C-metabolic flux analysis (13C-MFA), (ii) parameterizing a core kinetic model, and (iii) subsequently deploying an ensemble-docking workflow for discovering substrate-level regulations, this paper aims to reveal some of these factors and expand our knowledgebase governing C. thermocellum metabolism. Generated 13C labeling data were used with 13C-MFA to generate a wild-type flux distribution for the metabolic network. Notably, flux elucidation through MFA alluded to serine generation via the mercaptopyruvate pathway. Using the elucidated flux distributions in conjunction with batch fermentation process yield data for various mutant strains, we constructed a kinetic model of C. thermocellum core metabolism (i.e. k-ctherm138). Subsequently, we used the parameterized kinetic model to explore the effect of removing substrate-level regulations on ethanol yield and titer. Upon exploring all possible simultaneous (up to four) regulation removals we identified combinations that lead to many-fold model predicted improvement in ethanol titer. In addition, by coupling a systematic method for identifying putative competitive inhibitory mechanisms using K-FIT kinetic parameterization with the ensemble-docking workflow, we flagged 67 putative substrate-level inhibition mechanisms across central carbon metabolism supported by both kinetic formalism and docking analysis.
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Wang Y, Hu J, Li Y, Liu Z. Rare earth ion Nd3+ promotes production of cellulose ethanol by Clostridium thermocellum ATCC 27405. Polyhedron 2022. [DOI: 10.1016/j.poly.2021.115555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Li X, Han R, Bao T, Osire T, Zhang X, Xu M, Yang T, Rao Z. Citrulline deiminase pathway provides ATP and boosts growth of Clostridium carboxidivorans P7. BIOTECHNOLOGY FOR BIOFUELS 2021; 14:204. [PMID: 34656154 PMCID: PMC8520249 DOI: 10.1186/s13068-021-02051-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/30/2021] [Accepted: 10/02/2021] [Indexed: 06/13/2023]
Abstract
BACKGROUND Clostridium carboxidivorans P7 is capable of producing ethanol and butanol from inexpensive and non-food feedstock, such as syngas. Achieving improved ethanol and butanol production in the strain for industrial application depends on the energetics and biomass, especially ATP availability. RESULTS This study found that exogenous addition of citrulline promoted accumulation of ATP, increased specific growth rate, and reduced the doubling time of C. carboxidivorans P7. In heterotrophic fermentation experiments, the addition of citrulline increased intracellular ATP by 3.39-fold, significantly enhancing the production of total alcohol (ethanol + butanol) by 20%. Moreover, in the syngas fermentation experiments, the addition of citrulline improved the level of intracellular ATP and the biomass by 80.5% and 31.6%, respectively, resulting in an 18.6% and 60.3% increase in ethanol and the alcohol/acid production ratio, respectively. CONCLUSIONS This is the first report that citrulline could promote the growth of C. carboxidivorans P7 and increase the level of intracellular ATP, which is of great significance for the use of C. carboxidivorans P7 to synthesize biofuels.
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Affiliation(s)
- Xiangfei Li
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Rumeng Han
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Teng Bao
- Department of Chemical and Biomolecular Engineering, The Ohio State University, Columbus, OH, 43210, USA
| | - Tolbert Osire
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Xian Zhang
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Meijuan Xu
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China
| | - Taowei Yang
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China.
| | - Zhiming Rao
- The Key Laboratory of Industrial Biotechnology, Ministry of Education, School of Biotechnology, Jiangnan University, 1800 Lihu Road, Wuxi, 214122, Jiangsu, China.
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Srivastava RK, Akhtar N, Verma M, Imandi SB. Primary metabolites from overproducing microbial system using sustainable substrates. Biotechnol Appl Biochem 2020; 67:852-874. [PMID: 32294277 DOI: 10.1002/bab.1927] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 04/12/2020] [Indexed: 02/06/2023]
Abstract
Primary (or secondary) metabolites are produced by animals, plants, or microbial cell systems either intracellularly or extracellularly. Production capabilities of microbial cell systems for many types of primary metabolites have been exploited at a commercial scale. But the high production cost of metabolites is a big challenge for most of the bioprocess industries and commercial production needs to be achieved. This issue can be solved to some extent by screening and developing the engineered microbial systems via reconstruction of the genome-scale metabolic model. The predicted genetic modification is applied for an increased flux in biosynthesis pathways toward the desired product. Wherein the resulting microbial strain is capable of converting a large amount of carbon substrate to the expected product with minimum by-product formation in the optimal operating conditions. Metabolic engineering efforts have also resulted in significant improvement of metabolite yields, depending on the nature of the products, microbial cell factory modification, and the types of substrate used. The objective of this review is to comprehend the state of art for the production of various primary metabolites by microbial strains system, focusing on the selection of efficient strain and genetic or pathway modifications, applied during strain engineering.
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Affiliation(s)
- Rajesh K Srivastava
- Department of Biotechnology, GIT, GITAM (Deemed to be University), Gandhi Nagar Campus, Rushikonda, Visakhapatnam, India
| | - Nasim Akhtar
- Department of Biotechnology, GIT, GITAM (Deemed to be University), Gandhi Nagar Campus, Rushikonda, Visakhapatnam, India
| | - Malkhey Verma
- Departments of Biochemistry and Microbial Sciences, Central University of Punjab, Bathinda, India
| | - Sarat Babu Imandi
- Department of Biotechnology, GIT, GITAM (Deemed to be University), Gandhi Nagar Campus, Rushikonda, Visakhapatnam, India
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Adaptive laboratory evolution induced novel mutations in Zymomonas mobilis ATCC ZW658: a potential platform for co-utilization of glucose and xylose. ACTA ACUST UNITED AC 2020; 47:329-341. [DOI: 10.1007/s10295-020-02270-y] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2019] [Accepted: 03/02/2020] [Indexed: 01/22/2023]
Abstract
Abstract
A systematic adaptive laboratory evolution strategy was employed to develop a potential Zymomonas mobilis strain with the ability to co-utilize glucose and xylose. Z. mobilis ATCC ZW658, a recombinant xylose fermenting strain, was subjected to adaptive laboratory evolution over a period of 200 days under strict selection pressure of increasing concentration of xylose. The evolved strain exhibited 1.65 times increase in the overall specific xylose utilization rate when compared with the parent strain. Furthermore, the strain displayed significantly improved performance in terms of co-fermentation of xylose in the presence of glucose with specific glucose and xylose utilization rate of 1.24 g g−1 h−1 and 1.34 g g−1 h−1, respectively. Altered phenotypic response of the evolved strain, in terms of improved xylose utilization, co-utilization of mixed sugars, enhanced growth, ethanol production, and reduced xylitol production has been explained by novel mutations, identified using next-generation sequencing, in xylose assimilating, metabolizing, and crucial regulatory pathway genes and key enzyme activity assays.
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Ganguly J, Martin‐Pascual M, van Kranenburg R. CRISPR interference (CRISPRi) as transcriptional repression tool for Hungateiclostridium thermocellum DSM 1313. Microb Biotechnol 2020; 13:339-349. [PMID: 31802632 PMCID: PMC7017836 DOI: 10.1111/1751-7915.13516] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2019] [Revised: 11/06/2019] [Accepted: 11/12/2019] [Indexed: 01/13/2023] Open
Abstract
Hungateiclostridium thermocellum DSM 1313 has biotechnological potential as a whole-cell biocatalyst for ethanol production using lignocellulosic renewable sources. The full exploitation of H. thermocellum has been hampered due to the lack of simple and high-throughput genome engineering tools. Recently in our research group, a thermophilic bacterial CRISPR-Cas9-based system has been developed as a transcriptional suppression tool for regulation of gene expression. We applied ThermoCas9-based CRISPR interference (CRISPRi) to repress the H. thermocellum central metabolic lactate dehydrogenase (ldh) and phosphotransacetylase (pta) genes. The effects of repression on target genes were studied based on transcriptional expression and product formation. Single-guide RNA (sgRNA) under the control of native intergenic 16S/23S rRNA promoter from H. thermocellum directing the ThermodCas9 to the promoter region of both pta and ldh silencing transformants reduced expression up to 67% and 62% respectively. This resulted in 24% and 17% decrease in lactate and acetate production, correspondingly. Hence, the CRISPRi approach for H. thermocellum to downregulate metabolic genes can be used for remodelling of metabolic pathways without the requisite for genome engineering. These data established for the first time the feasibility of employing CRISPRi-mediated gene repression of metabolic genes in H. thermocellum DSM 1313.
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Affiliation(s)
| | - Maria Martin‐Pascual
- Laboratory of MicrobiologyWageningen UniversityStippeneng 46708WE WageningenThe Netherlands
| | - Richard van Kranenburg
- CorbionArkelsedijk 464206AC GorinchemThe Netherlands
- Laboratory of MicrobiologyWageningen UniversityStippeneng 46708WE WageningenThe 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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Engineering Clostridium for improved solvent production: recent progress and perspective. Appl Microbiol Biotechnol 2019; 103:5549-5566. [DOI: 10.1007/s00253-019-09916-7] [Citation(s) in RCA: 51] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2019] [Revised: 05/15/2019] [Accepted: 05/15/2019] [Indexed: 01/07/2023]
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Seo H, Lee JW, Garcia S, Trinh CT. Single mutation at a highly conserved region of chloramphenicol acetyltransferase enables isobutyl acetate production directly from cellulose by Clostridium thermocellum at elevated temperatures. BIOTECHNOLOGY FOR BIOFUELS 2019; 12:245. [PMID: 31636704 PMCID: PMC6792240 DOI: 10.1186/s13068-019-1583-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 10/01/2019] [Indexed: 05/03/2023]
Abstract
BACKGROUND Esters are versatile chemicals and potential drop-in biofuels. To develop a sustainable production platform, microbial ester biosynthesis using alcohol acetyltransferases (AATs) has been studied for decades. Volatility of esters endows high-temperature fermentation with advantageous downstream product separation. However, due to the limited thermostability of AATs known, the ester biosynthesis has largely relied on use of mesophilic microbes. Therefore, developing thermostable AATs is important for ester production directly from lignocellulosic biomass by the thermophilic consolidated bioprocessing (CBP) microbes, e.g., Clostridium thermocellum. RESULTS In this study, we engineered a thermostable chloramphenicol acetyltransferase from Staphylococcus aureus (CATSa) for enhanced isobutyl acetate production at elevated temperatures. We first analyzed the broad alcohol substrate range of CATSa. Then, we targeted a highly conserved region in the binding pocket of CATSa for mutagenesis. The mutagenesis revealed that F97W significantly increased conversion of isobutanol to isobutyl acetate. Using CATSa F97W, we demonstrated direct conversion of cellulose into isobutyl acetate by an engineered C. thermocellum at elevated temperatures. CONCLUSIONS This study highlights that CAT is a potential thermostable AAT that can be harnessed to develop the thermophilic CBP microbial platform for biosynthesis of designer bioesters directly from lignocellulosic biomass.
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Affiliation(s)
- Hyeongmin Seo
- Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, TN USA
- Center for Bioenergy Innovation (CBI), Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Jong-Won Lee
- Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville, TN USA
- Center for Bioenergy Innovation (CBI), Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Sergio Garcia
- Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, TN USA
- Center for Bioenergy Innovation (CBI), Oak Ridge National Laboratory, Oak Ridge, TN USA
| | - Cong T. Trinh
- Department of Chemical and Biomolecular Engineering, The University of Tennessee, Knoxville, TN USA
- Bredesen Center for Interdisciplinary Research and Graduate Education, The University of Tennessee, Knoxville, TN USA
- Center for Bioenergy Innovation (CBI), Oak Ridge National Laboratory, Oak Ridge, TN USA
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Liu YJ, Qi K, Zhang J, Chen C, Cui Q, Feng Y. Firmicutes-enriched IS 1447 represents a group of IS 3-family insertion sequences exhibiting unique + 1 transcriptional slippage. BIOTECHNOLOGY FOR BIOFUELS 2018; 11:300. [PMID: 30410575 PMCID: PMC6211511 DOI: 10.1186/s13068-018-1304-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/25/2018] [Accepted: 10/27/2018] [Indexed: 05/12/2023]
Abstract
BACKGROUND Bacterial insertion sequences (ISs) are ubiquitous mobile genetic elements that play important roles in genome plasticity, cell adaptability, and function evolution. ISs of various families and subgroups contain significantly diverse molecular features and functional mechanisms that are not fully understood. RESULTS IS1447 is a member of the widespread IS3 family and was previously detected to have transposing activity in a typical thermophilic and cellulolytic microorganism Clostridium thermocellum. Phylogenetic analysis showed that IS1447-like elements are widely distributed in Firmicutes and possess unique features in the IS3 family. Therefore, IS1447 may represent a novel subgroup of the IS3 family. Unlike other well-known IS3 subgroups performing programmed - 1 translational frameshifting for the expression of the transposase, IS1447 exhibits transcriptional slippage in both the + 1 and - 1 directions, each with a frequency of ~ 16%, and only + 1 slippage results in full-length and functional transposase. The slippage-prone region of IS1447 contains a run of nine A nucleotides following a stem-loop structure in mRNA, but mutagenesis analysis indicated that seven of them are sufficient for the observed slippage. Western blot analysis indicated that IS1447 produces three types of transposases with alternative initiations. Furthermore, the IS1447-subgroup elements are abundant in the genomes of several cellulolytic bacteria. CONCLUSION Our result indicated that IS1447 represents a new Firmicutes-enriched subgroup of the IS3 family. The characterization of the novel IS3-family member will enrich our understanding of the transposition behavior of IS elements and may provide insight into developing IS-based mutagenesis tools for thermophiles.
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Affiliation(s)
- Ya-Jun Liu
- CAS Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- Dalian National Laboratory for Clean Energy, Dalian, China
| | - Kuan Qi
- CAS Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- Dalian National Laboratory for Clean Energy, Dalian, China
- University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, China
| | - Jie Zhang
- CAS Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- Dalian National Laboratory for Clean Energy, Dalian, China
- University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing, China
- Present Address: Department of Biosystems Engineering, Auburn University, Auburn, AL 36849 USA
| | - Chao Chen
- CAS Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- Dalian National Laboratory for Clean Energy, Dalian, China
| | - Qiu Cui
- CAS Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- Dalian National Laboratory for Clean Energy, Dalian, China
| | - Yingang Feng
- CAS Key Laboratory of Biofuels, Shandong Provincial Key Laboratory of Energy Genetics, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of Sciences, Qingdao, China
- Dalian National Laboratory for Clean Energy, Dalian, China
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Enhanced ethanol formation by Clostridium thermocellum via pyruvate decarboxylase. Microb Cell Fact 2017; 16:171. [PMID: 28978312 PMCID: PMC5628457 DOI: 10.1186/s12934-017-0783-9] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 09/26/2017] [Indexed: 12/31/2022] Open
Abstract
Background Pyruvate decarboxylase (PDC) is a well-known pathway for ethanol production, but has not been demonstrated for high titer ethanol production at temperatures above 50 °C. Result Here we examined the thermostability of eight PDCs. The purified bacterial enzymes retained 20% of activity after incubation for 30 min at 55 °C. Expression of these PDC genes, except the one from Zymomonas mobilis, improved ethanol production by Clostridium thermocellum. Ethanol production was further improved by expression of the heterologous alcohol dehydrogenase gene adhA from Thermoanaerobacterium saccharolyticum. Conclusion The best PDC enzyme was from Acetobactor pasteurianus. A strain of C. thermocellum expressing the pdc gene from A. pasteurianus and the adhA gene from T. saccharolyticum was able to produce 21.3 g/L ethanol from 60 g/L cellulose, which is 70% of the theoretical maximum yield. Electronic supplementary material The online version of this article (doi:10.1186/s12934-017-0783-9) contains supplementary material, which is available to authorized users.
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Hon S, Olson DG, Holwerda EK, Lanahan AA, Murphy SJL, Maloney MI, Zheng T, Papanek B, Guss AM, Lynd LR. The ethanol pathway from Thermoanaerobacterium saccharolyticum improves ethanol production in Clostridium thermocellum. Metab Eng 2017; 42:175-184. [PMID: 28663138 DOI: 10.1016/j.ymben.2017.06.011] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2017] [Revised: 05/27/2017] [Accepted: 06/23/2017] [Indexed: 12/31/2022]
Abstract
Clostridium thermocellum ferments cellulose, is a promising candidate for ethanol production from cellulosic biomass, and has been the focus of studies aimed at improving ethanol yield. Thermoanaerobacterium saccharolyticum ferments hemicellulose, but not cellulose, and has been engineered to produce ethanol at high yield and titer. Recent research has led to the identification of four genes in T. saccharolyticum involved in ethanol production: adhE, nfnA, nfnB and adhA. We introduced these genes into C. thermocellum and observed significant improvements to ethanol yield, titer, and productivity. The four genes alone, however, were insufficient to achieve in C. thermocellum the ethanol yields and titers observed in engineered T. saccharolyticum strains, even when combined with gene deletions targeting hydrogen production. This suggests that other parts of T. saccharolyticum metabolism may also be necessary to reproduce the high ethanol yield and titer phenotype in C. thermocellum.
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Affiliation(s)
- Shuen Hon
- 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.
| | - Evert K Holwerda
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Anthony A Lanahan
- Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Sean J L Murphy
- 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
| | - Tianyong Zheng
- Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA; Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Beth Papanek
- Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA; Biosciences Division, 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; Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA; Bioenergy Science Center, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
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