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.

Automated summary

Our study provides evidence of H2S oxidation producing octasulfur globules via sulfide:quinone oxidoreductase (SQR) catalysis and spontaneous reactions in the bacterial cytoplasm. Understanding this process is important for geochemical cycling and supports the use of heterotrophic bacteria with SQR to oxidize toxic H2S into recoverable sulfur globules.