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 DSM 20294 with sulfide:quinone oxidoreductase (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 glutathione (GSH) to form GS(n)G (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 provide evidence of H(2)S 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 H(2)S into sulfur globules for recovery.