Sulfuroxidizing

Sulfuroxidizing, or sulfur oxidation, is the biological and chemical transformation of reduced sulfur compounds into sulfate. It encompasses both abiotic oxidation by oxygen or metal oxides and biotic oxidation carried out by sulfur-oxidizing organisms. In biology, sulfur-oxidizing bacteria and archaea obtain energy by oxidizing substrates such as hydrogen sulfide (H2S), elemental sulfur (S0), thiosulfate (S2O3^2−), and sulfite (SO3^2−) and often fix CO2 via autotrophic pathways. Common chemolithoautotrophs include Acidithiobacillus, Thiomonas, Thiobacillus, Beggiatoa, and the archaeon Sulfolobus; they inhabit acid mine drainages, hot springs, marine sediments, and other sulfide-rich habitats.

Two major enzymatic systems mediate sulfur oxidation. The Sox multienzyme system frequently oxidizes reduced sulfur compounds directly to sulfate, while the reverse dissimilatory sulfite reductase (rDSR) pathway operates in many sulfur-oxidizing bacteria that accumulate sulfur intermediates. Overall oxidation reactions convert reduced sulfur to sulfate, for example H2S + 2 O2 → SO4^2− + 2 H+. Partial oxidation can yield elemental sulfur or thiosulfate as intermediates.

Ecological and environmental significance: sulfur oxidation is integral to the global sulfur cycle and can influence pH, metal mobility, and community composition in sulfur-rich habitats. It underpins bioleaching and biomining, where SOB oxidize sulfide minerals to release metals, and is exploited in bioremediation of sulfide-contaminated waters and in microbial fuel cell technologies.