The pathway of sulfide oxidation to octasulfur globules in the cytoplasm of aerobic bacteria
Sulfur-oxidizing bacteria can oxidize hydrogen sulfide (H 2 S) 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 H 2 S into short-chain inorganic polysulfide (H 2 S n , n≥2) and organic polysulfide (RS n H, n≥2), which reacted with each other to form long-chain GS n H (n≥2) and H 2 S n before producing octasulfur (S 8 ), the main component of elemental sulfur. GS n H also reacted with GSH to form GSnG (n≥2) and H 2 S; H 2 S was again oxidized by SQR. After GSH was depleted, SQR simply oxidized H 2 S to H 2 S n , 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 H 2 S into relatively benign S 8 globules. IMPORTANCE Our results support a process of H 2 S 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 H 2 S into sulfur globules for recovery.