title: Se(VI) reduction and the precipitation of Se(0) by the facultative bacterium Enterobacter cloacae SLD1a-1 are regulated by FNR.
abstract: 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.
authors.affiliation: Department of Environmental Sciences, Rutgers University, 14 College Farm Rd., New Brunswick, NJ 07102, USA. nyee@envsci.rutgers.edu
authors.forename: N
authors.initials: N
authors.lastname: Yee
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.forename: A
authors.initials: A
authors.lastname: Dalia
authors.forename: T
authors.initials: T
authors.lastname: Boonfueng
authors.forename: D Y
authors.initials: DY
authors.lastname: Kobayashi
mesh_terms: D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D011232:Chemical Precipitation; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D016972:Enterobacter cloacae / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D015964:Gene Expression Regulation, Bacterial; D005816:Genetic Complementation Test; D007700:Kinetics; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D009154:Mutation; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D012643:Selenium / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D014157:Transcription Factors; D010088:Oxidoreductases; C078108:selenate reductase; D012643:Selenium