title: Formate-dependent H2 production by the mesophilic methanogen Methanococcus maripaludis.
abstract: Methanococcus maripaludis, an H(2)- and formate-utilizing methanogen, produced H(2) at high rates from formate. The rates and kinetics of H(2) production depended upon the growth conditions, and H(2) availability during growth was a major factor. Specific activities of resting cells grown with formate or H(2) were 0.4 to 1.4 U mg(-1) (dry weight). H(2) production in formate-grown cells followed Michaelis-Menten kinetics, and the concentration of formate required for half-maximal activity (K(f)) was 3.6 mM. In contrast, in H(2)-grown cells this process followed sigmoidal kinetics, and the K(f) was 9 mM. A key enzyme for formate-dependent H(2) production was formate dehydrogenase, Fdh. H(2) production and growth were severely reduced in a mutant containing a deletion of the gene encoding the Fdh1 isozyme, indicating that it was the primary Fdh. In contrast, a mutant containing a deletion of the gene encoding the Fdh2 isozyme possessed near-wild-type activities, indicating that this isozyme did not play a major role. H(2) production by a mutant containing a deletion of the coenzyme F(420)-reducing hydrogenase Fru was also severely reduced, suggesting that the major pathway of H(2) production comprised Fdh1 and Fru. Because a Deltafru-Deltafrc mutant retained 10% of the wild-type activity, an additional pathway is present. Mutants possessing deletions of the gene encoding the F(420)-dependent methylene-H(4)MTP dehydrogenase (Mtd) or the H(2)-forming methylene-H(4)MTP dehydrogenase (Hmd) also possessed reduced activity, which suggested that this second pathway was comprised of Fdh1-Mtd-Hmd. In contrast to H(2) production, the cellular rates of methanogenesis were unaffected in these mutants, which suggested that the observed H(2) production was not a direct intermediate of methanogenesis. In conclusion, high rates of formate-dependent H(2) production demonstrated the potential of M. maripaludis for the microbial production of H(2) from formate.
authors.affiliation: Department of Microbiology, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Boguslaw
authors.initials: B
authors.lastname: Lupa
authors.forename: Erik L
authors.initials: EL
authors.lastname: Hendrickson
authors.forename: John A
authors.initials: JA
authors.lastname: Leigh
authors.forename: William B
authors.initials: WB
authors.lastname: Whitman
mesh_terms: D005560:Formate Dehydrogenases / Q000235:genetics / Q000378:metabolism; D005561:Formates / Q000378:metabolism*; D017353:Gene Deletion; D006859:Hydrogen / Q000378:metabolism*; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D053858:Metabolic Networks and Pathways / Q000235:genetics; D008697:Methane / Q000378:metabolism; D017017:Methanococcus / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism
chemical_list: D005561:Formates; D007527:Isoenzymes; C030544:formic acid; D006859:Hydrogen; D010088:Oxidoreductases; C033895:coenzyme F420 hydrogenase; D005560:Formate Dehydrogenases; D008697:Methane
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