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 DSM20294 with 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 GSnH (n≥2) and H2Sn before producing octasulfur (S8), the main component of elemental sulfur. GSnH also reacted with 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 S8. S8 aggregated into sulfur globules in the cytoplasm. The results highlight the process of sulfide oxidation to S8 globules in the bacterial cytoplasm and demonstrate the potential of using heterotrophic bacteria with SQR to convert toxic H2S into relatively benign S8 globules. IMPORTANCE Our results support a process of H2S oxidation to produce octasulfur globules via 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.