title: Increase in ethanol yield via elimination of lactate production in an ethanol-tolerant mutant of Clostridium thermocellum.
abstract: Large-scale production of lignocellulosic biofuel is a potential solution to sustainably meet global energy needs. One-step consolidated bioprocessing (CBP) is a potentially advantageous approach for the production of biofuels, but requires an organism capable of hydrolyzing biomass to sugars and fermenting the sugars to ethanol at commercially viable titers and yields. Clostridium thermocellum, a thermophilic anaerobe, can ferment cellulosic biomass to ethanol and organic acids, but low yield, low titer, and ethanol sensitivity remain barriers to industrial production. Here, we deleted the hypoxanthine phosphoribosyltransferase gene in ethanol tolerant strain of C. thermocellum adhE*(EA) in order to allow use of previously developed gene deletion tools, then deleted lactate dehydrogenase (ldh) to redirect carbon flux towards ethanol. Upon deletion of ldh, the adhE*(EA) Δldh strain produced 30% more ethanol than wild type on minimal medium. The adhE*(EA) Δldh strain retained tolerance to 5% v/v ethanol, resulting in an ethanol tolerant platform strain of C. thermocellum for future metabolic engineering efforts.
authors: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America ; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America.
authors: Ranjita
authors: R
authors: Biswas
authors: Department of Bioengineering, University of California Berkeley, Berkeley, California, United States of America.
authors: Sandeep
authors: S
authors: Prabhu
authors: BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America ; Thayer School of Engineering at Dartmouth College, Hanover, New Hamphire, United States of America.
authors: Lee R
authors: LR
authors: Lynd
authors: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America ; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States of America.
authors: Adam M
authors: AM
authors: Guss
mesh_terms: D056804:Biofuels; D048013:Acetivibrio thermocellus / Q000235:genetics / Q000378:metabolism*; D000431:Ethanol / Q000378:metabolism*; D017353:Gene Deletion; D007041:Hypoxanthine Phosphoribosyltransferase / Q000235:genetics* / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism*; D060847:Metabolic Engineering
chemical_list: D056804:Biofuels; D019344:Lactic Acid; D000431:Ethanol; D007041:Hypoxanthine Phosphoribosyltransferase