A Molybdopterin Oxidoreductase Is Involved in H ₂ Oxidation in Desulfovibrio desulfuricans G20

Three mutants deficient in hydrogen/formate uptake were obtained through screening of a transposon mutant library containing 5,760 mutants of Desulfovibrio desulfuricans G20. Mutations were in the genes encoding the type I tetraheme cytochrome c 3 ( cycA ), Fe hydrogenase ( hydB ), and molybdopterin oxidoreductase ( mopB ). Mutations did not decrease the ability of cells to produce H 2 or formate during growth. Complementation of the cycA and mopB mutants with a plasmid carrying the intact cycA and/or mopB gene and the putative promoter from the parental strain allowed the recovery of H 2 uptake ability, showing that these specific genes are involved in H 2 oxidation. The mop operon encodes a periplasm-facing transmembrane protein complex which may shuttle electrons from periplasmic cytochrome c 3 to the menaquinone pool. Electrons can then be used for sulfate reduction in the cytoplasm.