title: Disruption of the operon encoding Ehb hydrogenase limits anabolic CO2 assimilation in the archaeon Methanococcus maripaludis.
abstract: Methanococcus maripaludis is a mesophilic archaeon that reduces CO2 to methane with H2 or formate as an energy source. It contains two membrane-bound energy-conserving hydrogenases, Eha and Ehb. To determine the role of Ehb, a deletion in the ehb operon was constructed to yield the mutant, strain S40. Growth of S40 was severely impaired in minimal medium. Both acetate and yeast extract were necessary to restore growth to nearly wild-type levels, suggesting that Ehb was involved in multiple steps in carbon assimilation. However, no differences in the total hydrogenase specific activities were found between the wild type and mutant in either cell extracts or membrane-purified fractions. Methanogenesis by resting cells with pyruvate as the electron donor was also reduced by 30% in S40, suggesting a defect in pyruvate oxidation. CO dehydrogenase/acetyl coenzyme A (CoA) synthase and pyruvate oxidoreductase had higher specific activities in the mutant, and genes encoding these enzymes, as well as AMP-forming acetyl-CoA synthetase, were expressed at increased levels. These observations support a role for Ehb in anabolic CO2 assimilation in methanococci.
authors.affiliation: Department of Microbiology, University of Georgia, Athens, Georgia 30602-2605, USA.
authors.forename: Iris
authors.initials: I
authors.lastname: Porat
authors.forename: Wonduck
authors.initials: W
authors.lastname: Kim
authors.forename: Erik L
authors.initials: EL
authors.lastname: Hendrickson
authors.forename: Qiangwei
authors.initials: Q
authors.lastname: Xia
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Tiansong
authors.initials: T
authors.lastname: Wang
authors.forename: Fred
authors.initials: F
authors.lastname: Taub
authors.forename: Brian C
authors.initials: BC
authors.lastname: Moore
authors.forename: Iain J
authors.initials: IJ
authors.lastname: Anderson
authors.forename: Murray
authors.initials: M
authors.lastname: Hackett
authors.forename: John A
authors.initials: JA
authors.lastname: Leigh
authors.forename: William B
authors.initials: WB
authors.lastname: Whitman
mesh_terms: D000106:Acetate-CoA Ligase / Q000378:metabolism; D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism*; D017353:Gene Deletion; D019766:Genes, Archaeal / Q000235:genetics; D006864:Hydrogenase / Q000235:genetics / Q000378:metabolism*; D008697:Methane / Q000378:metabolism; D017017:Methanococcus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D009876:Operon; D020543:Proteome / Q000378:metabolism; D050743:Pyruvate Synthase / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; D020543:Proteome; D002245:Carbon Dioxide; D006864:Hydrogenase; D000445:Aldehyde Oxidoreductases; D050743:Pyruvate Synthase; C019823:carbon monoxide dehydrogenase; D000106:Acetate-CoA Ligase; D008697:Methane