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Applied and Environmental Microbiology, September 2001, p. 3785-3794, Vol. 67, No. 9
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.9.3785-3794.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Identification and Characterization of Bacteria in a Selenium-Contaminated Hypersaline Evaporation Pond

M. P. de Souza,1 A. Amini,1 M. A. Dojka,1 I. J. Pickering,2 S. C. Dawson,1 N. R. Pace,dagger and N. Terry1,*

Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102,1 and Stanford Synchrotron Radiation Laboratory, Stanford Linear Accelerator Center, Menlo Park, California 94025-70152

Received 16 March 2001/Accepted 12 June 2001

Solar evaporation ponds are commonly used to reduce the volume of seleniferous agricultural drainage water in the San Joaquin Valley, Calif. These hypersaline ponds pose an environmental health hazard because they are heavily contaminated with selenium (Se), mainly in the form of selenate. Se in the ponds may be removed by microbial Se volatilization, a bioremediation process whereby toxic, bioavailable selenate is converted to relatively nontoxic dimethylselenide gas. In order to identify microbes that may be used for Se bioremediation, a 16S ribosomal DNA phylogenetic analysis of an aerobic hypersaline pond in the San Joaquin Valley showed that a previously unaffiliated group of uncultured bacteria (belonging to the order Cytophagales) was dominant, followed by a group of cultured gamma -Proteobacteria which was closely related to Halomonas species. Se K-edge X-ray absorption spectroscopy of selenate-treated bacterial isolates showed that they accumulated a mixture of predominantly selenate and a selenomethionine-like species, consistent with the idea that selenate was assimilated via the S assimilation pathway. One of these bacterial isolates (Halomonas-like strain MPD-51) was the best candidate for the bioremediation of hypersaline evaporation ponds contaminated with high Se concentrations because it tolerated 2 M selenate and 32.5% NaCl, grew rapidly in media containing selenate, and accumulated and volatilized Se at high rates (1.65 µg of Se g of protein-1 h-1), compared to other cultured bacterial isolates.

* Corresponding author. Mailing address: Department of Plant and Microbial Biology, 111 Koshland Hall, University of California, Berkeley, CA 94720-3102. Phone: (510) 642-3510. Fax: (510) 642-4995. E-mail: nterry{at}nature.berkeley.edu.

dagger Present address: Department of Molecular, Cellular and Developmental Biology, Campus Box 0347, University of Colorado, Boulder, CO 80309-0347.

Applied and Environmental Microbiology, September 2001, p. 3785-3794, Vol. 67, No. 9
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.9.3785-3794.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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