HYDROGEN SULFIDE PRODUCTION BY SYNECHOCOCCUS LIVIDUS Y52-s1

Under anaerobic conditions and in the absence of CO₂, the thermophilic blue-green alga Synechococcus lividus Y52-s, evolved hydrogen sulfide in both darkness and light. The mechanism of this process was investigated and compared with photo- and dark reductions in organisms representing several phyla. The photoproduction of H₂S from either sulfate or thiosulfate was inhibited by 3-(3,4-dichlorophenyl)-1, 1-dimethyl urea (DCMU) and carbonyl m-chlorophenyl-hydrazone (m-Cl-CCP). The inhibitory effect of DCMU showed the requirement for photosystem II as electron donor. Inhibition by m-Cl-CCP also implicated ATP as an energy source. Monofluoroacetate partially inhibited photoproduction of H₂S. This indicated that oxidative metabolism may act us a source of electrons to reduce the photooxidant under certain conditions. Thiosulfate acts only as electron acceptor and is reductively cleaved to S⁼ and SO₃⁼. Thiosulfate and sulfate appeared to replace CO₂ in the light and O₂ in darkness as electron acceptors. The phosphorylation uncouplers dinitrophenol and m-Cl-CCP stimulated dark H₂S production.