Kinetic oxygen isotope effects during dissimilatory sulfate reduction: A combined theoretical and experimental approach

Turchyn, Alexandra V. and Brüchert, Volker and Lyons, Timothy W. and Engel, Gregory S. and Balci, Nurgul and Schrag, Daniel P. and Brunner, Benjamin (2010) Kinetic oxygen isotope effects during dissimilatory sulfate reduction: A combined theoretical and experimental approach. Geochimica et Cosmochimica Acta, 74 (7). pp. 2011-2024. DOI 10.1016/j.gca.2010.01.004

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Abstract

Kinetic isotope effects related to the breaking of chemical bonds drive sulfur isotope fractionation during dissimilatory sulfate reduction (DSR), whereas oxygen isotope fractionation during DSR is dominated by exchange between intercellular sulfur intermediates and water. We use a simplified biochemical model for DSR to explore how a kinetic oxygen isotope effect may be expressed. We then explore these relationships in light of evolving sulfur and oxygen isotope compositions ([delta]34SSO4 and [delta]18OSO4) during batch culture growth of twelve strains of sulfate-reducing bacteria. Cultured under conditions to optimize growth and with identical [delta]18OH2O and initial [delta]18OSO4, all strains show 34S enrichment, whereas only six strains show significant 18O enrichment. The remaining six show no (or minimal) change in [delta]18OSO4 over the growth of the bacteria. We use these experimental and theoretical results to address three questions: (i) which sulfur intermediates exchange oxygen isotopes with water, (ii) what is the kinetic oxygen isotope effect related to the reduction of adenosine phosphosulfate (APS) to sulfite (SO32-), (iii) does a kinetic oxygen isotope effect impact the apparent oxygen isotope equilibrium values? We conclude that oxygen isotope exchange between water and a sulfur intermediate likely occurs downstream of APS and that our data constrain the kinetic oxygen isotope fractionation for the reduction of APS to sulfite to be smaller than 4[per mille sign]. This small oxygen isotope effect impacts the apparent oxygen isotope equilibrium as controlled by the extent to which APS reduction is rate-limiting.

Item Type: Article
Uncontrolled Keywords: 2010AREP, IA62;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Geochimica et Cosmochimica Acta
Volume: 74
Page Range: pp. 2011-2024
Identification Number: 10.1016/j.gca.2010.01.004
Depositing User: Sarah Humbert
Date Deposited: 28 Feb 2011 22:31
Last Modified: 23 Jul 2013 10:01
URI: http://eprints.esc.cam.ac.uk/id/eprint/2023

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