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Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway

Sim, Min Sub and Paris, Guillaume and Adkins, Jess F. and Orphan, Victoria J. and Sessions, Alex L. (2017) Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway. Geochimica et Cosmochimica Acta, 206 . pp. 57-72. ISSN 0016-7037.

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Microbial sulfate reduction exhibits a normal isotope effect, leaving unreacted sulfate enriched in ^(34)S and producing sulfide that is depleted in ^(34)S. However, the magnitude of sulfur isotope fractionation is quite variable. The resulting changes in sulfur isotope abundance have been used to trace microbial sulfate reduction in modern and ancient ecosystems, but the intracellular mechanism(s) underlying the wide range of fractionations remains unclear. Here we report the concentrations and isotopic ratios of sulfur metabolites in the dissimilatory sulfate reduction pathway of Desulfovibrio alaskensis. Intracellular sulfate and APS levels change depending on the growth phase, peaking at the end of exponential phase, while sulfite accumulates in the cell during stationary phase. During exponential growth, intracellular sulfate and APS are strongly enriched in ^(34)S. The fractionation between internal and external sulfate is up to 49‰, while at the same time that between external sulfate and sulfide is just a few permil. We interpret this pattern to indicate that enzymatic fractionations remain large but the net fractionation between sulfate and sulfide is muted by the closed-system limitation of intracellular sulfate. This ‘reservoir effect’ diminishes upon cessation of exponential phase growth, allowing the expression of larger net sulfur isotope fractionations. Thus, the relative rates of sulfate exchange across the membrane versus intracellular sulfate reduction should govern the overall (net) fractionation that is expressed. A strong reservoir effect due to vigorous sulfate reduction might be responsible for the well-established inverse correlation between sulfur isotope fractionation and the cell-specific rate of sulfate reduction, while at the same time intraspecies differences in sulfate uptake and/or exchange rates could account for the significant scatter in this relationship. Our approach, together with ongoing investigations of the kinetic isotope fractionation by key enzymes in the sulfate reduction pathway, should provide an empirical basis for a quantitative model relating the magnitude of microbial isotope fractionation to their environmental and physiological controls.

Item Type:Article
Related URLs:
URLURL TypeDescription
Sim, Min Sub0000-0002-3491-9002
Paris, Guillaume0000-0001-8368-1224
Adkins, Jess F.0000-0002-3174-5190
Orphan, Victoria J.0000-0002-5374-6178
Sessions, Alex L.0000-0001-6120-2763
Additional Information:© 2017 Elsevier Ltd. Received 30 July 2016, Accepted 18 February 2017, Available online 27 February 2017. This work was supported by an Agouron Geobiology Fellowship to MSS and the Gordon and Betty Moore Foundation Grant GBMF 3306 to VJO and ALS.
Funding AgencyGrant Number
Agouron InstituteUNSPECIFIED
Gordon and Betty Moore FoundationGBMF3306
Record Number:CaltechAUTHORS:20170227-143517457
Persistent URL:
Official Citation:Min Sub Sim, Guillaume Paris, Jess F. Adkins, Victoria J. Orphan, Alex L. Sessions, Quantification and isotopic analysis of intracellular sulfur metabolites in the dissimilatory sulfate reduction pathway, Geochimica et Cosmochimica Acta, Volume 206, 1 June 2017, Pages 57-72, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74554
Deposited By: Tony Diaz
Deposited On:27 Feb 2017 23:19
Last Modified:09 Mar 2020 13:19

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