Microbial oxidation of sulfur

Microbial oxidation of sulfur refers to the process by which microorganisms oxidize reduced sulfur compounds to obtain energy, often supporting autotrophic carbon fixation. This process is primarily carried out by chemolithoautotrophic sulfur-oxidizing prokaryotes, which use compounds such as hydrogen sulfide (H₂S), elemental sulfur (S⁰), thiosulfate (S₂O₃²⁻), and sulfite (SO₃²⁻) as electron donors. The oxidation of these substrates is typically coupled to the reduction of oxygen (O₂) or nitrate (NO₃⁻) as terminal electron acceptors. Under anaerobic conditions, some sulfur-oxidizing bacteria can use alternative oxidants, and certain phototrophic sulfur oxidizers derive energy from light while using sulfide or elemental sulfur as electron sources.

Several key microbial groups involved in sulfur oxidation include genera such as Beggiatoa, Thiobacillus, Acidithiobacillus, and Sulfurimonas, each adapted to specific redox conditions and environmental niches. Metabolic pathways like the Sox (sulfur oxidation) system, reverse dissimilatory sulfite reductase (rDSR) pathway, and the SQR (sulfide:quinone oxidoreductase) pathway are discussed as central mechanisms through which these microbes mediate sulfur transformations.

Microbial sulfur oxidation plays a major role in the biogeochemical cycling of sulfur and contributes to nutrient dynamics in environments hosting both abundant reduced sulfur species and low concentrations of oxygen. These include marine sediments, hydrothermal vents, cold seeps, sulfidic caves, oxygen minimum zones (OMZs), and stratified water columns. Microbial communities are structured by local biogeochemical gradients and their sulfur-oxidizing activity links carbon and nitrogen cycling in suboxic or anoxic environments. Through their metabolic versatility and ecological distribution, sulfur-oxidizing microorganisms help maintain redox balance and influence the chemistry of their surrounding environments, supporting broader ecosystem functioning.