Dataset Information

A mutation in the AdhE alcohol dehydrogenase of Clostridium thermocellum increases tolerance to several primary alcohols, including isobutanol, n-butanol and ethanol.

ABSTRACT: Clostridium thermocellum is a good candidate organism for producing cellulosic biofuels due to its native ability to ferment cellulose, however its maximum biofuel titer is limited by tolerance. Wild type C. thermocellum is inhibited by 5?g/L n-butanol. Using growth adaptation in a chemostat, we increased n-butanol tolerance to 15?g/L. We discovered that several tolerant strains had acquired a D494G mutation in the adhE gene. Re-introducing this mutation recapitulated the n-butanol tolerance phenotype. In addition, it increased tolerance to several other primary alcohols including isobutanol and ethanol. To confirm that adhE is the cause of inhibition by primary alcohols, we showed that deleting adhE also increases tolerance to several primary alcohols.

SUBMITTER: Tian L

PROVIDER: S-EPMC6370804 | biostudies-literature | 2019 Feb

REPOSITORIES: biostudies-literature

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A mutation in the AdhE alcohol dehydrogenase of Clostridium thermocellum increases tolerance to several primary alcohols, including isobutanol, n-butanol and ethanol.

Tian Liang L Cervenka Nicholas D ND Low Aidan M AM Olson Daniel G DG Lynd Lee R LR

Scientific reports 20190211 1

Clostridium thermocellum is a good candidate organism for producing cellulosic biofuels due to its native ability to ferment cellulose, however its maximum biofuel titer is limited by tolerance. Wild type C. thermocellum is inhibited by 5 g/L n-butanol. Using growth adaptation in a chemostat, we increased n-butanol tolerance to 15 g/L. We discovered that several tolerant strains had acquired a D494G mutation in the adhE gene. Re-introducing this mutation recapitulated the n-butanol tolerance phe ...[more]

PMID: 30741948

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Project description:UNLABELLED:Thermoanaerobacterium saccharolyticum and Clostridium thermocellum are anaerobic thermophilic bacteria being investigated for their ability to produce biofuels from plant biomass. The bifunctional alcohol and aldehyde dehydrogenase gene, adhE, is present in these bacteria and has been known to be important for ethanol formation in other anaerobic alcohol producers. This study explores the inactivation of the adhE gene in C. thermocellum and T. saccharolyticum. Deletion of adhE reduced ethanol production by >95% in both T. saccharolyticum and C. thermocellum, confirming that adhE is necessary for ethanol formation in both organisms. In both adhE deletion strains, fermentation products shifted from ethanol to lactate production and resulted in lower cell density and longer time to reach maximal cell density. In T. saccharolyticum, the adhE deletion strain lost >85% of alcohol dehydrogenase (ADH) activity. Aldehyde dehydrogenase (ALDH) activity did not appear to be affected, although ALDH activity was low in cell extracts. Adding ubiquinone-0 to the ALDH assay increased activity in the T. saccharolyticum parent strain but did not increase activity in the adhE deletion strain, suggesting that ALDH activity was inhibited. In C. thermocellum, the adhE deletion strain lost >90% of ALDH and ADH activity in cell extracts. The C. thermocellum adhE deletion strain contained a point mutation in the lactate dehydrogenase gene, which appears to deregulate its activation by fructose 1,6-bisphosphate, leading to constitutive activation of lactate dehydrogenase. IMPORTANCE:Thermoanaerobacterium saccharolyticum and Clostridium thermocellum are bacteria that have been investigated for their ability to produce biofuels from plant biomass. They have been engineered to produce higher yields of ethanol, yet questions remain about the enzymes responsible for ethanol formation in these bacteria. The genomes of these bacteria encode multiple predicted aldehyde and alcohol dehydrogenases which could be responsible for alcohol formation. This study explores the inactivation of adhE, a gene encoding a bifunctional alcohol and aldehyde dehydrogenase. Deletion of adhE reduced ethanol production by >95% in both T. saccharolyticum and C. thermocellum, confirming that adhE is necessary for ethanol formation in both organisms. In strains without adhE, we note changes in biochemical activity, product formation, and growth.

Project description:Clostridium thermocellum and Thermoanaerobacterium saccharolyticum are thermophilic bacteria that have been engineered to produce ethanol from the cellulose and hemicellulose fractions of biomass, respectively. Although engineered strains of T. saccharolyticum produce ethanol with a yield of 90% of the theoretical maximum, engineered strains of C. thermocellum produce ethanol at lower yields (?50% of the theoretical maximum). In the course of engineering these strains, a number of mutations have been discovered in their adhE genes, which encode both alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) enzymes. To understand the effects of these mutations, the adhE genes from six strains of C. thermocellum and T. saccharolyticum were cloned and expressed in Escherichia coli, the enzymes produced were purified by affinity chromatography, and enzyme activity was measured. In wild-type strains of both organisms, NADH was the preferred cofactor for both ALDH and ADH activities. In high-ethanol-producing (ethanologen) strains of T. saccharolyticum, both ALDH and ADH activities showed increased NADPH-linked activity. Interestingly, the AdhE protein of the ethanologenic strain of C. thermocellum has acquired high NADPH-linked ADH activity while maintaining NADH-linked ALDH and ADH activities at wild-type levels. When single amino acid mutations in AdhE that caused increased NADPH-linked ADH activity were introduced into C. thermocellum and T. saccharolyticum, ethanol production increased in both organisms. Structural analysis of the wild-type and mutant AdhE proteins was performed to provide explanations for the cofactor specificity change on a molecular level.This work describes the characterization of the AdhE enzyme from different strains of C. thermocellum and T. saccharolyticum. C. thermocellum and T. saccharolyticum are thermophilic anaerobes that have been engineered to make high yields of ethanol and can solubilize components of plant biomass and ferment the sugars to ethanol. In the course of engineering these strains, several mutations arose in the bifunctional ADH/ALDH protein AdhE, changing both enzyme activity and cofactor specificity. We show that changing AdhE cofactor specificity from mostly NADH linked to mostly NADPH linked resulted in higher ethanol production by C. thermocellum and T. saccharolyticum.

Dataset Information

A mutation in the AdhE alcohol dehydrogenase of Clostridium thermocellum increases tolerance to several primary alcohols, including isobutanol, n-butanol and ethanol.

Publications

A mutation in the AdhE alcohol dehydrogenase of Clostridium thermocellum increases tolerance to several primary alcohols, including isobutanol, n-butanol and ethanol.

Similar Datasets

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