title: Engineering electron metabolism to increase ethanol production in Clostridium thermocellum.
abstract: The NfnAB (NADH-dependent reduced ferredoxin: NADP+oxidoreductase) and Rnf (ion-translocating reduced ferredoxin: NAD+oxidoreductase) complexes are thought to catalyze electron transfer between reduced ferredoxin and NAD(P)+. Efficient electron flux is critical for engineering fuel production pathways, but little is known about the relative importance of these enzymes in vivo. In this study we investigate the importance of the NfnAB and Rnf complexes in Clostridium thermocellum for growth on cellobiose and Avicel using gene deletion, enzyme assays, and fermentation product analysis. The NfnAB complex does not seem to play a major role in metabolism, since deletion of nfnAB genes had little effect on the distribution of fermentation products. By contrast, the Rnf complex appears to play an important role in ethanol formation. Deletion of rnf genes resulted in a decrease in ethanol formation. Overexpression of rnf genes resulted in an increase in ethanol production of about 30%, but only in strains where the hydG hydrogenase maturation gene was also deleted.
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Lo
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
authors.forename: Daniel G
authors.initials: DG
authors.lastname: Olson
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
authors.forename: Sean Jean-Loup
authors.initials: SJ
authors.lastname: Murphy
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Tian
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
authors.forename: Shuen
authors.initials: S
authors.lastname: Hon
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA.
authors.forename: Anthony
authors.initials: A
authors.lastname: Lanahan
authors.affiliation: BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA; Biosciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA.
authors.forename: Adam M
authors.initials: AM
authors.lastname: Guss
authors.affiliation: Thayer School of Engineering, Dartmouth College, Hanover, NH 03755, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak Ridge TN 37830, USA. Electronic address: Lee.R.Lynd@Dartmouth.edu.
authors.forename: Lee R
authors.initials: LR
authors.lastname: Lynd
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D053898:Biosynthetic Pathways / Q000502:physiology; D048013:Acetivibrio thermocellus / Q000502:physiology*; D004579:Electron Transport / Q000502:physiology*; D000431:Ethanol / Q000302:isolation & purification / Q000378:metabolism*; D024861:Genetic Enhancement / Q000379:methods*; D060847:Metabolic Engineering / Q000379:methods*; D053858:Metabolic Networks and Pathways / Q000502:physiology
chemical_list: D001426:Bacterial Proteins; D000431:Ethanol
keywords: Clostridium thermocellum; Ethanol