Sulfur isotope fractionation by Proteus vulgaris and Salmonella heidelberg during the reduction of thiosulfate.

Proteus vulgaris metabolized thiosulfate to H2S. The amount evolved and its sulfur isotope composition identified it solely with sulfane sulfur. In contrast, Salmonella heidelberg sequentially reduced the sulfane sulfur of S2O3(-2) with slight enrichment of the evolved sulfide in 32S and then reduced the sulfonate sulfur of S2O3(-2) with large isotopic selectivities and an inverse isotopic fractionation pattern. The inverse isotope fractionation pattern for the H2S derived from the sulfonate sulfur was almost identical to that observed during the reduction of high concentrations of sulfite by S. heidelberg.