Abstract
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.