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

• Published in: Applied and Environmental Microbiology Vol. 73; no. 6; pp. 1914 - 1920
• Main Authors: Yee, N, Ma, J, Dalia, A, Boonfueng, T, Kobayashi, D.Y
• Format: Journal Article
• Language: English
• Published: Washington, DC American Society for Microbiology 01.03.2007
• Subjects: Bacterial Proteins - metabolism; Bacteriology; Base Sequence; Biochemistry; Biological and medical sciences; Chemical Precipitation; Cloning, Molecular; DNA, Bacterial - chemistry; DNA, Bacterial - genetics; E coli; Enterobacter cloacae; Enterobacter cloacae - genetics; Enterobacter cloacae - metabolism; Escherichia coli; Escherichia coli - genetics; Escherichia coli - metabolism; Fundamental and applied biological sciences. Psychology; Gene Expression; Gene Expression Regulation, Bacterial; Genes; Genetic Complementation Test; Kinetics; Microbiology; Microscopy, Electron, Scanning; Molecular Sequence Data; Mutation; Oxidation-Reduction; Oxidoreductases - metabolism; Physiology and Biotechnology; Selenium - metabolism; Sequence Analysis, DNA; Transcription Factors - metabolism; Bacteria; Precipitation; Reduction; Regulation(control); Enterobacter cloacae; Enterobacteriaceae
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.02542-06

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.