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Applied and Environmental Microbiology, September 2009, p. 5621-5630, Vol. 75, No. 17
0099-2240/09/$08.00+0     doi:10.1128/AEM.02948-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Sulfur Isotope Enrichment during Maintenance Metabolism in the Thermophilic Sulfate-Reducing Bacterium Desulfotomaculum putei{triangledown}

Mark M. Davidson,1 M. E. Bisher,2 Lisa M. Pratt,3 Jon Fong,3 Gordon Southam,4 Susan M. Pfiffner,5 Z. Reches,6 and Tullis C. Onstott1*

Department of Geosciences, Guyot Hall, Princeton University, Princeton, New Jersey 08544,1 Molecular Biology Department, Moffett Lab, Princeton University, Princeton, New Jersey,2 Department of Geology, Indiana University, Bloomington, Indiana 47405-1405,3 Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada N6A 5B7,4 Center for Biomarker Analysis, University of Tennessee, Knoxville, Tennessee,5 School of Geology and Geophysics, University of Oklahoma, Norman, Oklahoma6

Received 27 December 2008/ Accepted 19 June 2009

Values of {Delta}34S (Formula, where {delta}34SHS and Formula indicate the differences in the isotopic compositions of the HS– and SO42– in the eluent, respectively) for many modern marine sediments are in the range of –55 to –75{per thousand}, much greater than the –2 to –46{per thousand} {varepsilon}34S (kinetic isotope enrichment) values commonly observed for microbial sulfate reduction in laboratory batch culture and chemostat experiments. It has been proposed that at extremely low sulfate reduction rates under hypersulfidic conditions with a nonlimited supply of sulfate, isotopic enrichment in laboratory culture experiments should increase to the levels recorded in nature. We examined the effect of extremely low sulfate reduction rates and electron donor limitation on S isotope fractionation by culturing a thermophilic, sulfate-reducing bacterium, Desulfotomaculum putei, in a biomass-recycling culture vessel, or "retentostat." The cell-specific rate of sulfate reduction and the specific growth rate decreased progressively from the exponential phase to the maintenance phase, yielding average maintenance coefficients of 10–16 to 10–18 mol of SO4 cell–1 h–1 toward the end of the experiments. Overall S mass and isotopic balance were conserved during the experiment. The differences in the {delta}34S values of the sulfate and sulfide eluting from the retentostat were significantly larger, attaining a maximum {Delta}34S of –20.9{per thousand}, than the –9.7{per thousand} observed during the batch culture experiment, but differences did not attain the values observed in marine sediments.

* Corresponding author. Mailing address: Department of Geosciences, Princeton University, Princeton, NJ 08544. Phone: (609) 258-7678. Fax: (609) 258-1274. E-mail: tullis{at}princeton.edu

{triangledown} Published ahead of print on 26 June 2009.

Applied and Environmental Microbiology, September 2009, p. 5621-5630, Vol. 75, No. 17
0099-2240/09/$08.00+0     doi:10.1128/AEM.02948-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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