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Applied and Environmental Microbiology, September 2000, p. 3711-3721, Vol. 66, No. 9
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Modeling Reduction of Uranium U(VI) under Variable Sulfate Concentrations by Sulfate-Reducing Bacteria

John R. Spear,* Linda A. Figueroa, and Bruce D. Honeyman

Division of Environmental Science and Engineering, Colorado School of Mines, Golden, Colorado 80401

Received 4 February 2000/Accepted 22 June 2000

The kinetics for the reduction of sulfate alone and for concurrent uranium [U(VI)] and sulfate reduction, by mixed and pure cultures of sulfate-reducing bacteria (SRB) at 21 ± 3°C were studied. The mixed culture contained the SRB Desulfovibrio vulgaris along with a Clostridium sp. determined via 16S ribosomal DNA analysis. The pure culture was Desulfovibrio desulfuricans (ATCC 7757). A zero-order model best fit the data for the reduction of sulfate from 0.1 to 10 mM. A lag time occurred below cell concentrations of 0.1 mg (dry weight) of cells/ml. For the mixed culture, average values for the maximum specific reaction rate, Vmax, ranged from 2.4 ± 0.2 µmol of sulfate/mg (dry weight) of SRB · h-1) at 0.25 mM sulfate to 5.0 ± 1.1 µmol of sulfate/mg (dry weight) of SRB · h-1 at 10 mM sulfate (average cell concentration, 0.52 mg [dry weight]/ml). For the pure culture, Vmax was 1.6 ± 0.2 µmol of sulfate/mg (dry weight) of SRB · h-1 at 1 mM sulfate (0.29 mg [dry weight] of cells/ml). When both electron acceptors were present, sulfate reduction remained zero order for both cultures, while uranium reduction was first order, with rate constants of 0.071 ± 0.003 mg (dry weight) of cells/ml · min-1 for the mixed culture and 0.137 ± 0.016 mg (dry weight) of cells/ml · min-1 (U0 = 1 mM) for the D. desulfuricans culture. Both cultures exhibited a faster rate of uranium reduction in the presence of sulfate and no lag time until the onset of U reduction in contrast to U alone. This kinetics information can be used to design an SRB-dominated biotreatment scheme for the removal of U(VI) from an aqueous source.

* Corresponding author. Present address: Department of Molecular, Cellular, and Developmental Biology, Campus Box 347, University of Colorado, Boulder, Boulder, CO 80309. Phone: (303) 735-1808. Fax: (303) 492-7744. E-mail: spearj{at}colorado.edu.

Applied and Environmental Microbiology, September 2000, p. 3711-3721, Vol. 66, No. 9
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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