Fig 6.

Schematic representation of electron flow during MSR through hydrogen cycling in Gram-negative sulfate-reducing bacteria that oxidize lactate (41, 49, 54). Malate is also oxidized via pyruvate, but the transfer of reducing equivalents from the first oxidation step of malate may differ from that of lactate oxidation (44). Many enzymes and electron carriers involved in this process, from the cytoplasm to the periplasm, contain iron in their active sites (45, 58). Iron limitation impairs the synthesis of cytochromes and hydrogenases (55), reducing the flow of electrons to the sulfate reduction system. Abbreviations: LacP, lactate permease; Ldh, lactate dehydrogenase; Por, pyruvate-ferredoxin oxidoreductase; Hase, hydrogenase; Cyt. c, cytochrome c; SulP, sulfate permease; Sat, ATP sulfurylase; Apr, APS reductase; Dsr, dissimilatory sulfite reductase; PPase, pyrophosphate phosphatase.