Sulfur isotope fractionation during bacterial reduction and disproportionation of thiosulfate and sulfite

• Published in: Geochimica et cosmochimica acta Vol. 62; no. 15; pp. 2585 - 2595
• Main Authors: Habicht, Kirsten S, Canfield, Donald E, Rethmeier, J̈org
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-08-1998
• ISSN: 0016-7037; 1872-9533
• DOI: 10.1016/S0016-7037(98)00167-7

In bacterial cultures we measured sulfur isotope fractionation during transformations of thiosulfate (S
2O
3
2−) and sulfite (SO
3
2−), pathways which may be of considerable importance in the cycling of sulfur in marine sediments and euxinic waters. We documented isotope fractionations during the reduction and disproportionation of S
2O
3
2− and SO
3
2− by bacterial enrichments and pure bacterial cultures from marine and freshwater environments. We also measured the isotope fractionation associated with the anoxygenic phototrophic oxidation of H
2S to S
2O
3
2− by cyanobacteria. Except for SO
3
2− reduction, isotope fractionations for these processes have not been previously reported. During the dissimilatory reduction of SO
3
2−, H
2S was depleted in
34S by 6‰, and during the reduction of S
2O
3
2− to H
2S, depletions were between 7‰ and 11‰. The largest observed isotope fractionation was associated with the bacterial disproportionation of SO
3
2− which caused a
34S depletion in H
2S of 20–37‰ and a
34S enrichment in sulfate of 7–12‰. During the bacterial disproportionation of S
2O
3
2−, isotope fractionations between the outer sulfane sulfur and H
2S and between the inner sulfonate sulfur and SO
4
2− were <4‰. We observed isotope exchange between the two sulfur atoms of S
2O
3
2− leading to a depletion of
34S in H
2S by up to 12‰ with a comparable enrichment of
34S in SO
4
2−. No isotope fractionation was associated with the anoxygenic phototrophic oxidation of H
2S to S
2O
3
2−. The depletion of
34S into H
2S during the bacterial reduction and disproportionation of S
2O
3
2− and SO
3
2− may, in addition to sulfate reduction and the bacterial disproportionation of elemental sulfur, contribute to the generation of
34S-depleted sedimentary sulfides.