Sulphur isotope fractionation during the reduction of elemental sulphur and thiosulphate by Dethiosulfovibrio spp.

Abstract

Stable sulphur isotope fractionation was investigated during reduction of thiosulphate and elemental sulphur at 28°C by growing batch cultures of the sulphur- and thiosulphate-reducing bacteria Dethiosulfovibrio marinus (type strain DSM 12537) and Dethiosulfovibrio russensis (type strain DSM 12538), using citrate as carbon and energy source. The cell-specific thiosulphate reduction rate in the growth phase was 7.4±3.9 fmol cell−1 d−1. The hydrogen sulphide produced was enriched in 32S by 10.3±1 ‰ compared with total thiosulphate sulphur, close to previous experimental results observed for other sulphate- and non-sulphate-reducing bacteria. Elemental sulphur reduction yields sulphur isotope enrichment factors between−1.3 and−5.2 ‰ for D. russensis and−1.7 and−5.1 ‰ for D. marinus. The smaller fractionation effects are observed in the exponential growth phase (cellular rates between 5 and 70 fmol S° cell−1 d−1) and enhanced discrimination under conditions of citrate depletion and cell lysis (cellular rates between 0.3 and 3 fmol S° cell−1 d−1).