Sulfur isotope fractionation during growth of sulfate-reducing bacteria on various carbon sources

Stable sulfur isotope fractionation during microbial sulfate reduction is a potential tool to estimate sulfate reduction rates at field sites. However, little is known about the influence of the utilized carbon source on the magnitude of sulfur isotope fractionation. To investigate this effect, both a pure culture (strain PRTOL1) and enrichment cultures from a petroleum hydrocarbon (PHC)-contaminated aquifer were used and,grown in batch cultures on various carbon sources with an initial sulfate concentration of I mmol/L. As sole carbon sources the PHC components naphthalene, 1,3,5-trimethylbenzene, and heating oil (enrichment culture) and the organic acids acetate, pyruvate, benzoate, and 3-phenylpropionate (enrichment Culture and PRTOL1) were used. Sulfate reduction rates of all cultures ranged from 6 +/- 1 nmol cm(-3) d(-1) (enrichment culture grown on 1,15-trimethylbetizene) to 280 +/- 6 nmol cm-3 d(-1) (enrichment culture grown on pyruvate). Cell-specific sulfate reduction rates ranged from 1.1 x 10(-14) Mol cell(-1) d(-1) (PRTOL1 grown oil pyruvate) to 1.5 x 10(-13) mol cell(-1) d(-1) (PRTOL1 grown on acetate). Sulfur isotope enrichment factors (epsilon) for the enrichment culture ranged from 16.1parts per thousand (3-phenylpropionate) to 34.5parts per thousand (1,3,5-trimethylbenzene) and for PRTOL1 from 30.0parts per thousand (benzoate) to 36.0parts per thousand (pyruvate). Cultures of PRTOL1 always showed higher epsilon values than the enrichment culture when grown on the same carbon source due to culture-specific properties. Higher E values were obtained when the enrichment culture was grown on PHC components than on organic acids. No relationship between epsilon values and cell-specific sulfate reduction rate existed when all data were combined. When comparing the magnitude of epsilon values determined in this laboratory study with epsilon values measured at contaminated and uncontaminated field sites, it becomes evident that a Multitude of factors influences epsilon values at field sites and complicates their interpretation. The results of this study help us assess some of the general parameters that govern the magnitude of epsilon in sulfate-reducing environments. Copyright (C) 2004 Elsevier Ltd.