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Applied and Environmental Microbiology, March 2007, p. 1914-1920, Vol. 73, No. 6
0099-2240/07/$08.00+0     doi:10.1128/AEM.02542-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Se(VI) Reduction and the Precipitation of Se(0) by the Facultative Bacterium Enterobacter cloacae SLD1a-1 Are Regulated by FNR{triangledown}

N. Yee,1* J. Ma,1 A. Dalia,2 T. Boonfueng,3 and D. Y. Kobayashi2

Department of Environmental Sciences,1 Department of Plant Biology and Pathology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey,2 Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, New Jersey3

Received 31 October 2006/ Accepted 6 January 2007

The fate of selenium in the environment is controlled, in part, by microbial selenium oxyanion reduction and Se(0) precipitation. In this study, we identified a genetic regulator that controls selenate reductase activity in the Se-reducing bacterium Enterobacter cloacae SLD1a-1. Heterologous expression of the global anaerobic regulatory gene fnr (fumarate nitrate reduction regulator) from E. cloacae in the non-Se-reducing strain Escherichia coli S17-1 activated the ability to reduce Se(VI) and precipitate insoluble Se(0) particles. Se(VI) reduction by E. coli S17-1 containing the fnr gene occurred at rates similar to those for E. cloacae, with first-order reaction constants of k = 2.07 x 10–2 h–1 and k = 3.36 x 10–2 h–1, respectively, and produced elemental selenium particles with identical morphologies and short-range atomic orders. Mutation of the fnr gene in E. cloacae SLD1a-1 resulted in derivative strains that were deficient in selenate reductase activity and unable to precipitate elemental selenium. Complementation by the wild-type fnr sequence restored the ability of mutant strains to reduce Se(VI). Our findings suggest that Se(VI) reduction and the precipitation of Se(0) by facultative anaerobes are regulated by oxygen-sensing transcription factors and occur under suboxic conditions.

* Corresponding author. Mailing address: Department of Environmental Sciences, Rutgers University, 14 College Farm Rd., New Brunswick, NJ 07102. Phone: (732) 932-1105. Fax: (732) 932-8644. E-mail: nyee{at}envsci.rutgers.edu.

{triangledown} Published ahead of print on 19 January 2007.

Applied and Environmental Microbiology, March 2007, p. 1914-1920, Vol. 73, No. 6
0099-2240/07/$08.00+0     doi:10.1128/AEM.02542-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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