title: Membrane Complexes ofSyntrophomonas wolfeiInvolved in Syntrophic Butyrate Degradation and Hydrogen Formation.
abstract: Syntrophic butyrate metabolism involves the thermodynamically unfavorable production of hydrogen and/or formate from the high potential electron donor, butyryl-CoA. Such redox reactions can occur only with energy input by a process called reverse electron transfer. Previous studies have demonstrated that hydrogen production from butyrate requires the presence of a proton gradient, but the biochemical machinery involved has not been clearly elucidated. In this study, the gene and enzyme systems involved in reverse electron transfer bySyntrophomonas wolfeiwere investigated using proteomic and gene expression approaches.S. wolfeiwas grown in co-culture withMethanospirillum hungateiorDehalococcoides mccartyiunder conditions requiring reverse electron transfer and compared to both axenicS. wolfeicultures and co-cultures grown in conditions that do not require reverse electron transfer. Blue native gel analysis of membranes solubilized from syntrophically grown cells revealed the presence of a membrane-bound hydrogenase, Hyd2, which exhibited hydrogenase activity during in gel assays. Bands containing a putative iron-sulfur (FeS) oxidoreductase were detected in membranes of crotonate-grown and butyrate grownS. wolfeicells. The genes for the corresponding hydrogenase subunits,hyd2ABC, were differentially expressed at higher levels during syntrophic butyrate growth when compared to growth on crotonate. The expression of the FeS oxidoreductase gene increased whenS. wolfeiwas grown withM. hungatei. Additional membrane-associated proteins detected included FoF1ATP synthase subunits and several membrane transporters that may aid syntrophic growth. Furthermore, syntrophic butyrate metabolism can proceed exclusively by interspecies hydrogen transfer, as demonstrated by growth withD. mccartyi, which is unable to use formate. These results argue for the importance of Hyd2 and FeS oxidoreductase in reverse electron transfer during syntrophic butyrate degradation.
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK, USA.
authors.forename: Bryan R
authors.initials: BR
authors.lastname: Crable
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK, USA.
authors.forename: Jessica R
authors.initials: JR
authors.lastname: Sieber
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley CA, USA.
authors.forename: Xinwei
authors.initials: X
authors.lastname: Mao
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley, Berkeley CA, USA.
authors.forename: Lisa
authors.initials: L
authors.lastname: Alvarez-Cohen
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics, University of California, Los Angeles, Los Angeles CA, USA.
authors.forename: Robert
authors.initials: R
authors.lastname: Gunsalus
authors.affiliation: Department of Biological Chemistry, University of California, Los Angeles, Los Angeles CA, USA.
authors.forename: Rachel R
authors.initials: RR
authors.lastname: Ogorzalek Loo
authors.affiliation: Department of Biological Chemistry, University of California, Los Angeles, Los Angeles CA, USA.
authors.forename: Hong
authors.initials: H
authors.lastname: Nguyen
authors.affiliation: Department of Microbiology and Plant Biology, University of Oklahoma, Norman OK, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McInerney
keywords: biohydrogen; fatty acids; hydrogenase; methanogenesis; syntrophy