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Elucidating central metabolic redox obstacles hindering ethanol production in Clostridium thermocellum

Journal Article · · Metabolic Engineering
 [1];  [2];  [1];  [3];  [3];  [1]
  1. The Univ. of Tennessee, Knoxville, TN (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); The Univ. of Tennessee, Knoxville, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Dartmouth College, Hanover, NH (United States)
Clostridium thermocellum is an anaerobic, Gram-positive, thermophilic bacterium that has generated great interest due to its ability to ferment lignocellulosic biomass to ethanol. However, ethanol production is low due to the complex and poorly understood branched metabolism of C. thermocellum, and in some cases overflow metabolism as well. In this work, we developed a predictive stoichiometric metabolic model for C. thermocellum which incorporates the current state of understanding, with particular attention to cofactor specificity in the atypical glycolytic enzymes and the complex energy, redox, and fermentative pathways with the goal of aiding metabolic engineering efforts. We validated the model s capability to encompass experimentally observed phenotypes for the parent strain and derived mutants designed for significant perturbation of redox and energy pathways. Metabolic flux distributions revealed significant alterations in key metabolic branch points (e.g., phosphoenol pyruvate, pyruvate, acetyl-CoA, and cofactor nodes) in engineered strains for channeling electron and carbon fluxes for enhanced ethanol synthesis, with the best performing strain doubling ethanol yield and titer compared to the parent strain. In silico predictions of a redox-imbalanced genotype incapable of growth were confirmed in vivo, and a mutant strain was used as a platform to probe redox bottlenecks in the central metabolism that hinder efficient ethanol production. The results highlight the robustness of the redox metabolism of C. thermocellum and the necessity of streamlined electron flux from reduced ferredoxin to NAD(P)H for high ethanol production. The model was further used to design a metabolic engineering strategy to phenotypically constrain C. thermocellum to achieve high ethanol yields while requiring minimal genetic manipulations. Furthermore, the model can be applied to design C. thermocellum as a platform microbe for consolidated bioprocessing to produce ethanol and other reduced metabolites.
Research Organization:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States). BioEnergy Science Center (BESC)
Sponsoring Organization:
USDOE Office of Science (SC), Biological and Environmental Research (BER); USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Grant/Contract Number:
AC05-00OR22725
OSTI ID:
1327638
Alternate ID(s):
OSTI ID: 1250937
Journal Information:
Metabolic Engineering, Journal Name: Metabolic Engineering Journal Issue: C Vol. 32; ISSN 1096-7176
Publisher:
ElsevierCopyright Statement
Country of Publication:
United States
Language:
English

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Cited By (7)

Rex in Caldicellulosiruptor bescii : Novel regulon members and its effect on the production of ethanol and overflow metabolites journal April 2018
Exploring complex cellular phenotypes and model-guided strain design with a novel genome-scale metabolic model of Clostridium thermocellum DSM 1313 implementing an adjustable cellulosome journal September 2016
Single mutation at a highly conserved region of chloramphenicol acetyltransferase enables isobutyl acetate production directly from cellulose by Clostridium thermocellum at elevated temperatures journal October 2019
Overflow metabolism and growth cessation in Clostridium thermocellum DSM1313 during high cellulose loading fermentations : Overflow Metabolism and Growth Cessation in journal August 2017
Specialized activities and expression differences for Clostridium thermocellum biofilm and planktonic cells journal February 2017
Improved growth rate in Clostridium thermocellum hydrogenase mutant via perturbed sulfur metabolism journal January 2017
Development of a core Clostridium thermocellum kinetic metabolic model consistent with multiple genetic perturbations journal May 2017

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