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Applied and Environmental Microbiology, October 2006, p. 6514-6526, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.01066-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Dissimilatory Arsenate and Sulfate Reduction in Sediments of Two Hypersaline, Arsenic-Rich Soda Lakes: Mono and Searles Lakes, California

T. R. Kulp,1 S. E. Hoeft,1 L. G. Miller,1 C. Saltikov,2 J. N. Murphy,2 S. Han,3 B. Lanoil,3 and R. S. Oremland1*

U.S. Geological Survey, Menlo Park, California 94025,1 Department of Environmental Toxicology, University of California at Santa Cruz, Santa Cruz, California 95064,2 Department of Environmental Sciences, University of California at Riverside, Riverside, California 925213

Received 9 May 2006/ Accepted 31 July 2006

A radioisotope method was devised to study bacterial respiratory reduction of arsenate in sediments. The following two arsenic-rich soda lakes in California were chosen for comparison on the basis of their different salinities: Mono Lake (~90 g/liter) and Searles Lake (~340 g/liter). Profiles of arsenate reduction and sulfate reduction were constructed for both lakes. Reduction of [73As]arsenate occurred at all depth intervals in the cores from Mono Lake (rate constant [k] = 0.103 to 0.04 h–1) and Searles Lake (k = 0.012 to 0.002 h–1), and the highest activities occurred in the top sections of each core. In contrast, [35S]sulfate reduction was measurable in Mono Lake (k = 7.6 x104 to 3.2 x 10–6 h–1) but not in Searles Lake. Sediment DNA was extracted, PCR amplified, and separated by denaturing gradient gel electrophoresis (DGGE) to obtain phylogenetic markers (i.e., 16S rRNA genes) and a partial functional gene for dissimilatory arsenate reduction (arrA). The amplified arrA gene product showed a similar trend in both lakes; the signal was strongest in surface sediments and decreased to undetectable levels deeper in the sediments. More arrA gene signal was observed in Mono Lake and was detectable at a greater depth, despite the higher arsenate reduction activity observed in Searles Lake. A partial sequence (about 900 bp) was obtained for a clone (SLAS-3) that matched the dominant DGGE band found in deeper parts of the Searles Lake sample (below 3 cm), and this clone was found to be closely related to SLAS-1, a novel extremophilic arsenate respirer previously cultivated from Searles Lake.

* Corresponding author. Mailing address: U.S. Geological Survey, Menlo Park, CA 94025. Phone: (650) 329-4482. Fax: (650) 329-4463. E-mail: roremlan{at}usgs.gov.

Applied and Environmental Microbiology, October 2006, p. 6514-6526, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.01066-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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