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Mangalo, M. ; Meckenstock, R.U. ; Stichler, W. ; Einsiedl, F.

Stable isotope fractionation during bacterial sulfate reduction is controlled by reoxidation of intermediates.

Geochim. Cosmochim. Acta 71, 4161-4171 (2007)
DOI PMC
Open Access Green möglich sobald Postprint bei der ZB eingereicht worden ist.
Bacterial sulfate reduction is one of the most important respiration processes in anoxic habitats and is often assessed by analyzing the results of stable isotope fractionation. However, stable isotope fractionation is supposed to be influenced by the reduction rate and other parameters, such as temperature. We studied here the mechanistic basics of observed differences in stable isotope fractionation during bacterial sulfate reduction. Batch experiments with four sulfate-reducing strains (Desulfovibrio desulfuricans, Desulfobacca acetoxidans, Desulfonatronovibrio hydrogenovorans, and strain TRM1) were performed. These microorganisms metabolize different carbon sources (lactate, acetate, formate, and toluene) and showed broad variations in their sulfur isotope enrichment factors. We performed a series of experiments on isotope exchange of 18O between residual sulfate and ambient water. Batch experiments were conducted with 18O-enriched (delta18Owater = +700‰) and depleted water (delta18Owater = -40‰), respectively, and the stable 18O isotope shift in the residual sulfate was followed. For Desulfovibrio desulfuricans and Desulfonatronovibrio hydrogenovorans, which are both characterized by low sulfur isotope fractionation (S > -13.2‰), delta18O values in the remaining sulfate increased by only 50‰ during growth when 18O-enriched water was used for the growth medium. In contrast, with Desulfobacca acetoxidans and strain TRM1 (S < -22.7‰) the residual sulfate showed an increase of the sulfate delta18O close to the values of the enriched water of +700‰. In the experiments with ?18O-depleted water, the oxygen isotope values in the residual sulfate stayed fairly constant for strains Desulfovibrio desulfuricans, Desulfobacca acetoxidans and Desulfonatronovibrio hydrogenovorans. However, strain TRM1, which exhibits the lowest sulfur isotope fractionation factor (S < -38.7‰) showed slightly decreasing delta18O values.Our results give strong evidence that the oxygen atoms of sulfate exchange with water during sulfate reduction. However, this neither takes place in the sulfate itself nor during formation of APS (adenosine-5'-phosphosulfate), but rather in intermediates of the sulfate reduction pathway. These may in turn be partially reoxidized to form sulfate. This reoxidation leads to an incorporation of oxygen from water into the “recycled” sulfate changing the overall 18O isotopic composition of the remaining sulfate fraction. Our study shows that such incorporation of 18O is correlated with the stable isotope enrichment factor for sulfur measured during sulfate reduction. The reoxidation of intermediates of the sulfate reduction pathway does also strongly influence the sulfur stable isotope enrichment factor. This aforesaid reoxidation is probably dependent on the metabolic conversion of the substrate and therefore also influences the stable isotope fractionation factor indirectly in a rate dependent manner. However, this effect is only indirect. The sulfur isotope enrichment factors for the kinetic reactions themselves are probably not rate dependent.
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Publikationstyp Artikel: Journalartikel
Dokumenttyp Wissenschaftlicher Artikel
Korrespondenzautor
ISSN (print) / ISBN 0016-7037
e-ISSN 1872-9533
Zeitschrift Geochimica et Cosmochimica Acta
Quellenangaben Band: 71, Heft: 17, Seiten: 4161-4171 Artikelnummer: , Supplement: ,
Verlag Elsevier
Nichtpatentliteratur Publikationen
Begutachtungsstatus Peer reviewed
Institut(e) Institute of Groundwater Ecology (IGOE)