The Heterotrophic Bacterium Cupriavidus pinatubonensis JMP134 Oxidizes Sulfide to Sulfate with Thiosulfate as a Key Intermediate.

Heterotrophic bacteria actively participate in the biogeochemical cycle of sulfur on Earth. The heterotrophic bacterium JMP134 contains several enzymes involved in sulfur oxidation, but how these enzymes work together to oxidize sulfide in the bacterium has not been studied. Using gene-deletion and whole-cell assays, we determined that the bacterium uses sulfide:quinone oxidoreductase to oxidize sulfide to polysulfide, which is further oxidized to sulfite by persulfide dioxygenase. Sulfite spontaneously reacts with polysulfide to produce thiosulfate. The sulfur-oxidizing (Sox) system oxidizes thiosulfate to sulfate. Flavocytochrome sulfide dehydrogenase enhances thiosulfate oxidation by the Sox system but couples with the Sox system for sulfide oxidation to sulfate in the absence of sulfide:quinone oxidoreductase. Thus, JMP134 contains a main pathway and a contingent pathway for sulfide oxidation. We establish a new pathway of sulfide oxidation with thiosulfate as a key intermediate in JMP134. The bacterium mainly oxidizes sulfide by using sulfide:quinone oxidoreductase, persulfide dioxygenase, and the Sox system with thiosulfate as a key intermediate. Although the purified and reconstituted Sox system oxidizes sulfide, its rate of sulfide oxidation in JMP134 is too low to be physiologically relevant. The findings reveal how these sulfur-oxidizing enzymes participate in sulfide oxidation in a single bacterium.