title: Elimination of formate production in Clostridium thermocellum.
abstract: The ability of Clostridium thermocellum to rapidly degrade cellulose and ferment resulting hydrolysis products into ethanol makes it a promising platform organism for cellulosic biofuel production via consolidated bioprocessing. Currently, however, ethanol yield is far below theoretical maximum due to branched product pathways that divert carbon and electrons towards formate, H2, lactate, acetate, and secreted amino acids. To redirect carbon and electron flux away from formate, genes encoding pyruvate:formate lyase (pflB) and PFL-activating enzyme (pflA) were deleted. Formate production in the resulting Δpfl strain was eliminated and acetate production decreased by 50 % on both complex and defined medium. The growth rate of the Δpfl strain decreased by 2.9-fold on defined medium and biphasic growth was observed on complex medium. Supplementation of defined medium with 2 mM formate restored Δpfl growth rate to 80 % of the parent strain. The role of pfl in metabolic engineering strategies and C1 metabolism is discussed.
authors.affiliation: Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rydzak
authors.forename: Lee R
authors.initials: LR
authors.lastname: Lynd
authors.forename: Adam M
authors.initials: AM
authors.lastname: Guss
mesh_terms: D000085:Acetates / Q000378:metabolism; D000123:Acetyltransferases / Q000235:genetics; D000596:Amino Acids / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics; D056804:Biofuels; D019149:Bioreactors; D002244:Carbon / Q000378:metabolism; D048013:Acetivibrio thermocellus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D004798:Enzymes / Q000235:genetics; D000431:Ethanol / Q000378:metabolism; D005561:Formates / Q000378:metabolism*; D055786:Gene Knockout Techniques; D019344:Lactic Acid / Q000378:metabolism; D060847:Metabolic Engineering
chemical_list: D000085:Acetates; D000596:Amino Acids; D001426:Bacterial Proteins; D056804:Biofuels; D004798:Enzymes; D005561:Formates; C030544:formic acid; D019344:Lactic Acid; D000431:Ethanol; D002244:Carbon; D000123:Acetyltransferases; C040285:pyruvate formate-lyase activating enzyme; C022560:formate C-acetyltransferase