title: Stable sulfur and oxygen isotope fractionation of anoxic sulfide oxidation by two different enzymatic pathways.
abstract: The microbial oxidation of sulfide is a key reaction of the microbial sulfur cycle, recycling sulfur in its most reduced valence state back to more oxidized forms usable as electron acceptors. Under anoxic conditions, nitrate is a preferential electron acceptor for this process. Two enzymatic pathways have been proposed for sulfide oxidation under nitrate reducing conditions, the sulfide:quinone oxidoreductase (SQR) pathway and the Sox (sulfur oxidation) system. In experiments with the model strains Thiobacillus denitrificans and Sulfurimonas denitrificans, both pathways resulted in a similar small sulfur and oxygen isotope fractionation of -2.4 to -3.6‰ for (34)S and -2.4 to -3.4‰ for (18)O. A similar pattern was detected during the oxidation of sulfide in a column percolated with sulfidic, nitrate amended groundwater. In experiments with (18)O-labeled water, a strong oxygen isotope fractionation was observed for T. denitrificans and S. denitrificans, indicating a preferential incorporation of (18)O-depleted oxygen released as water by nitrate reduction to nitrogen. The study indicates that nitrate-dependent sulfide oxidation might be monitored in the environment by analysis of (18)O-depleted sulfate.
authors.affiliation: Department of Isotope Biogeochemistry, Helmholtz-Centre for Environmental Research UFZ , Permoserstraße 15, 04318 Leipzig, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Poser
authors.forename: Carsten
authors.initials: C
authors.lastname: Vogt
authors.forename: Kay
authors.initials: K
authors.lastname: Knöller
authors.forename: Jörg
authors.initials: J
authors.lastname: Ahlheim
authors.forename: Holger
authors.initials: H
authors.lastname: Weiss
authors.forename: Sabine
authors.initials: S
authors.lastname: Kleinsteuber
authors.forename: Hans-H
authors.initials: HH
authors.lastname: Richnow
mesh_terms: D020565:Epsilonproteobacteria / Q000378:metabolism*; D009566:Nitrates / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D010103:Oxygen Isotopes / Q000378:metabolism*; D011808:Quinone Reductases / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism; D013440:Sulfides / Q000378:metabolism*; D013460:Sulfur Isotopes / Q000378:metabolism*; D013855:Thiobacillus / Q000378:metabolism*; D050862:Oxidoreductases Acting on Sulfur Group Donors
chemical_list: D009566:Nitrates; D010088:Oxidoreductases; D010103:Oxygen Isotopes; D011808:Quinone Reductases; D013431:Sulfates; D013440:Sulfides; D013460:Sulfur Isotopes; D050862:Oxidoreductases Acting on Sulfur Group Donors; C073412:sulfide quinone reductase