Anaerobic bacteria have different ways to evolve hydrogen, two of them are directly coupled to pyruvate oxidation. First, the pyruvate:formate lyase system (present for example in enterobacteria) oxidizes pyruvate to acetyl-CoA and formate and the latter is then split by a hydrogenlyaseintohydrogenandcarbondioxide.Second, the pyruvate:ferredoxin oxidoreductase (present for example in clostridia) oxidizes pyruvate to acetyl-CoA, carbondioxideandreducedferredoxin.Bothsystemshave in common that the precursors have redox potentials low