The effect of sulfur compounds on H2 evolution/consumption reactions, mediated by various hydrogenases, in the purple sulfur bacterium, Thiocapsa roseopersicina.

The influence of reduced sulfur compounds (including stored S(0)) on H(2) evolution/consumption reactions in the purple sulfur bacterium, Thiocapsa roseopersicina BBS, was studied using mutants containing only one of the three known [NiFe] hydrogenase enzymes: Hox, Hup or Hyn. The observed effects depended on the kind of hydrogenase involved. The mutant harbouring Hox hydrogenase was able to use S(2)O (3) (2-) , SO (3) (2-) , S(2-) and S(0) as electron donors for light-dependent H(2) production. Dark H(2) evolution from organic substrates via Hox hydrogenase was inhibited by S(0). Under light conditions, endogenous H(2) uptake by Hox or Hup hydrogenases was suppressed by S compounds. CO(2)-dependent H(2) uptake by Hox hydrogenase in the light required the additional presence of S compounds, unlike the Hup-mediated process. Dark H(2) consumption via Hyn hydrogenase was connected to utilization of S(0) as an electron acceptor and resulted in the accumulation of H(2)S. In wild type BBS, with high levels of stored S(0), dark H(2) production from organic substrates was significantly lower, but H(2)S accumulation significantly higher, than in the mutant GB1121(Hox(+)). There is a possibility that H(2) produced via Hox hydrogenase is consumed by Hyn hydrogenase to reduce S(0).