The Pathway of Sulfide Oxidation to Octasulfur Globules in the Cytoplasm of Aerobic Bacteria

Sulfur-oxidizing bacteria can oxidize hydrogen sulfide (H2S) to produce sulfur globules. Although the process is common, the pathway is unclear. In recombinant Escherichia coli and wild-type Corynebacterium vitaeruminis DSM 20294 with sulfide:quinone oxidoreductase (SQR) but no enzymes to oxidize zero valence sulfur, SQR oxidized H2S into short-chain inorganic polysulfide (H2Sn, n >= 2) and organic polysulfide (RSnH, n >= 2), which reacted with each other to form long-chain GS(n)H (n >= 2) and H2Sn before producing octasulfur (S-8), the main component of elemental sulfur. GS(n)H also reacted with glutathione (GSH) to form GSnG (n >= 2) and H2S; H2S was again oxidized by SQR. After GSH was depleted, SQR simply oxidized H2S to H2Sn, which spontaneously generated S-8. S-8 aggregated into sulfur globules in the cytoplasm. The results highlight the process of sulfide oxidation to S-8 globules in the bacterial cytoplasm and demonstrate the potential of using heterotrophic bacteria with SQR to convert toxic H2S into relatively benign S-8 globules. IMPORTANCE Our results provide evidence of H2S oxidation producing octasulfur globules via sulfide:quinone oxidoreductase (SQR) catalysis and spontaneous reactions in the bacterial cytoplasm. Since the process is an important event in geochemical cycling, a better understanding facilitates further studies and provides theoretical support for using heterotrophic bacteria with SQR to oxidize toxic H2S into sulfur globules for recovery.