Elimination of hydrogenase active site assembly blocks H2 production and increases ethanol yield in Clostridium thermocellum

Ranjita Biswas, Tianyong Zheng, Daniel G. Olson, Lee R. Lynd, Adam M. Guss

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92 Scopus citations

Abstract

Background: The native ability of Clostridium thermocellum to rapidly consume cellulose and produce ethanol makes it a leading candidate for a consolidated bioprocessing (CBP) biofuel production strategy. C. thermocellum also synthesizes lactate, formate, acetate, H2, and amino acids that compete with ethanol production for carbon and electrons. Elimination of H2 production could redirect carbon flux towards ethanol production by making more electrons available for acetyl coenzyme A reduction to ethanol. Results: H2 production in C. thermocellum is encoded by four hydrogenases. Rather than delete each individually, we targeted hydrogenase maturase gene hydG, involved in converting the three [FeFe] hydrogenase apoenzymes into holoenzymes. Further deletion of the [NiFe] hydrogenase (ech) resulted in a mutant that functionally lacks all four hydrogenases. H2 production in δhydGδech was undetectable, and the ethanol yield nearly doubled to 64% of the maximum theoretical yield. Genomic analysis of δhydG revealed a mutation in adhE, resulting in a strain with both NADH- and NADPH-dependent alcohol dehydrogenase activities. While this same adhE mutation was found in ethanol-tolerant C. thermocellum strain E50C, δhydG and δhydGδech are not more ethanol tolerant than the wild type, illustrating the complicated interactions between redox balancing and ethanol tolerance in C. thermocellum. Conclusions: The dramatic increase in ethanol production suggests that targeting protein post-translational modification is a promising new approach for simultaneous inactivation of multiple enzymes.

Original languageEnglish
Article number20
JournalBiotechnology for Biofuels
Volume8
Issue number1
DOIs
StatePublished - Feb 12 2015

Funding

This work was supported by the BioEnergy Science Center, U.S. DOE Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. DOE under contract DE-AC05-00OR22725. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes.

Keywords

  • Cellulosic ethanol
  • Clostridium thermocellum
  • Hydrogenase maturation
  • Metabolic engineering

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