Large sulfur isotope fractionation by bacterial sulfide oxidation

Abstract

A sulfide-oxidizing microorganism, <i>Desulfurivibrio alkaliphilus</i> (DA), generates a consistent enrichment of sulfur-34 (³⁴ <i>S</i>) in the produced sulfate of +12.5 per mil or greater. This observation challenges the general consensus that the microbial oxidation of sulfide does not result in large ³⁴ <i>S</i> enrichments and suggests that sedimentary sulfides and sulfates may be influenced by metabolic activity associated with sulfide oxidation. Since the DA-type sulfide oxidation pathway is ubiquitous in sediments, in the modern environment, and throughout Earth history, the enrichments and depletions in ³⁴ <i>S</i> in sediments may be the combined result of three microbial metabolisms: microbial sulfate reduction, the disproportionation of external sulfur intermediates, and microbial sulfide oxidation.