FIG 1.

(A) Anaerobic formate metabolism in S. oneidensis MR-1. The model depicts oxidation of lactate (or pyruvate) as the sole carbon and energy source coupled to reduction of fumarate via the periplasmic fumarate reductase FccA. Two electrons are generated by lactate dehydrogenase (LDH) from the conversion of lactate into pyruvate. These electrons enter the menaquinone pool (MK) in the inner membrane (IM) directly or indirectly, depending on which of the LDH enzymes catalyze the reaction as S. oneidensis has different systems for d- and l-lactate (11, 13). (B) Genomic organization of genes directly involved in formate metabolism in MR-1. Genes encoding the α, β, and γ subunits of an FDH complex are colored yellow, green, and blue, respectively. fdhX genes, which encode small proteins of unknown function, are colored pink. The accessory genes involved in FDH complex maturation are colored orange, and the genes involved in cofactor maturation (selAB), formate transport (focA), and the hyd operon are colored purple.