Cupriavidus necator H16 Uses Flavocytochrome Sulfide Dehydrogenase To Oxidize Self-Produced and Added Sulfide.

Production of sulfide (HS, HS, and S) by heterotrophic bacteria during aerobic growth is a common phenomenon. Some bacteria with sulfide:quinone oxidoreductase (SQR) and persulfide dioxygenase (PDO) can oxidize self-produced sulfide to sulfite and thiosulfate, but other bacteria without these enzymes release sulfide into the medium, from which HS can volatilize into the gas phase. Here, we report that H16, with the and genes encoding flavocytochrome sulfide dehydrogenases (FCSDs), also oxidized self-produced HS. A mutant in which and were deleted accumulated and released HS. When and were expressed in strain Pa3K with deletions of its and genes, the recombinant rapidly oxidized sulfide to sulfane sulfur. When PDO was also cloned into the recombinant, the recombinant with both FCSD and PDO oxidized sulfide to sulfite and thiosulfate. Thus, the proposed pathway is similar to the pathway catalyzed by SQR and PDO, in which FCSD oxidizes sulfide to polysulfide, polysulfide spontaneously reacts with reduced glutathione (GSH) to produce glutathione persulfide (GSSH), and PDO oxidizes GSSH to sulfite, which chemically reacts with polysulfide to produce thiosulfate. About 20.6% of sequenced bacterial genomes contain SQR, and only 3.9% contain FCSD. This is not a surprise, since SQR is more efficient in conserving energy because it passes electrons from sulfide oxidation into the electron transport chain at the quinone level, while FCSD passes electrons to cytochrome The transport of electrons from the latter to O conserves less energy. FCSDs are grouped into three subgroups, well conserved at the taxonomic level. Thus, our data show the diversity in sulfide oxidation by heterotrophic bacteria. Heterotrophic bacteria with SQR and PDO can oxidize self-produced sulfide and do not release HS into the gas phase. H16 has FCSD but not SQR, and it does not release HS. We confirmed that the bacterium used FCSD for the oxidation of self-produced sulfide. The bacterium also oxidized added sulfide. The common presence of SQRs, FCSDs, and PDOs in heterotrophic bacteria suggests the significant role of heterotrophic bacteria in sulfide oxidation, participating in sulfur biogeochemical cycling. Further, FCSDs have been identified in anaerobic photosynthetic bacteria and chemolithotrophic bacteria, but their physiological roles are unknown. We showed that heterotrophic bacteria use FCSDs to oxidize self-produced sulfide and extraneous sulfide, and they may be used for HS bioremediation.