Role of the Hya hydrogenase in recycling of anaerobically produced H2 in Salmonella enterica serovar Typhimurium.

Double and triple uptake-type hydrogenase mutants were used to determine which hydrogenase recycles fermentatively produced hydrogen. The Deltahyb Deltahya and Deltahyd Deltahya double mutants evolved H(2) at rates similar to that of the triple mutant strain, so Hya alone oxidizes the bulk of H(2) produced during fermentation. When only Hya was present, no hydrogen production was observed in nutrient-limited medium. H(2) uptake assays showed that Hya can oxidize both exogenously added H(2) and formate hydrogen lyase-evolved H(2) anaerobically. Even after anaerobic growth, all three uptake-type hydrogenases could function in the presence of oxygen, including using O(2) as a terminal acceptor.