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| Titel |
Combined S-33 and O-18 Isotope Tracing of Intracellular Sulfur Metabolism during Microbial Sulfate Reduction |
| VerfasserIn |
Gilad Antler, Tanja Bosak, Shuhei Ono, Orit Sivan, Alexandra V. Turchyn |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250093963
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| Publikation (Nr.) |
 EGU/EGU2014-9204.pdf |
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| Zusammenfassung |
| Microbial sulfate reduction is a key player in the global carbon cycle, oxidizing nearly 50%
of organic matter in marine sediments. The biochemical pathway of microbial sulfate
reduction fractionates sulfur and oxygen isotopes and these fractionations can be used to
reconstruct S cycling in sediments. Sulfur isotope fractionation during microbial sulfate
reduction, which partitions lighter sulfur (32S) into sulfide and heavier sulfur (33S and 34S)
into the residual sulfate, can be as high as 72ofor 34S/32S. The availability and type of
organic substrate control the magnitude of sulfur isotope fractionation by influencing the
fluxes of and the transfer of electrons to different S species. The partitioning of oxygen in
sulfate during microbial sulfate reduction appears to be strongly influenced by the
oxygen isotopic composition of water in which the bacteria grow, but its magnitude
also seems to correlate with the magnitude of 34S/32S isotope fractionation. In
addition, the fractionation of 33S/32S is thought to reflect the reversibility of some
intercellular fluxes. We wanted to investigate whether the 18O/16O, 34S/32S and
33S/32S isotope fractionations in sulfate are controlled by the same intracellular
processes and conditions. This was done by investigating the combined sulfur and
oxygen isotope partitioning by a marine Desulfovibrio sp. grown in pure culture on
different organic substrates and in water with different isotopic composition of
oxygen.
The isotope fractionations of oxygen and sulfur correlated with the cell specific sulfate
reduction rates (csSRR), where slower rates yielded higher sulfur fractionation (as high as
60) and higher oxygen isotope fractionation. The trends in 33S/32S and 34S/32S with the
changing csSRR was similar to the trends in 18O/16O with the csSRR, suggesting that the
same intercellular pathways controlled both oxygen and sulfur isotope signatures during
microbial sulfate reduction. The use of water with different isotopic composition of oxygen
showed that the kinetic isotopic fractionation was negligible and that δ18O in sulfate
should be 22.5ohigher than δ18O in water (at 22°C). This relationship indicates
that more intracellular sulfite may be oxidized back to sulfate when the flux of
electrons from the electron donor to sulfite is low, allowing isotopic exchange of
oxygen between sulfite and water. The use of our experimental results as constraints
in a reactive transport model implies that the magnitudes of the oxygen isotope
fractionation and sulfur isotope fractionation are correlated under a broad range of
sulfate reduction rates in marine and marginal marine environments. This correlation
suggests a strong role for the electron donor in controlling the intracellular redox
fluxes of sulfur and the fractionation of oxygen isotopes in the natural environment. |
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