Tuesday, November 14, 2006
178-17
Heterologous Expression of the fnr Gene from Enterobacter Cloacae SLD1-1a in Escherichia coli S17-1 Activates Selenate Reductase Activity and the Ability to Precipitate Se(0) Biominerals.
Nathan Yee and Donald Kobayashi. Rutgers Univ, Dept Environmental Sciences, New Brunswick, NJ 08901
The fate of selenium in the environment is controlled, in part, by microbial selenium oxyanion reduction and Se(0) biomineral formation. Enzymatic reduction of soluble selenate [Se(VI), SeO42-] and selenite [Se(IV), SeO32-] to less toxic Se(0) converts selenium into insoluble mineral form. However, despite the ubiquity of Se-reducing bacteria in soils and sediments, the mechanisms of Se(0) biomineralization are poorly understood. In this study, we identify a genetic pathway that confers selenate reductase activity in the common soil bacterium Enterobacter cloacae. Using a direct cloning approach, we show that heterologous expression of the global anaerobic regulatory gene fnr from Enterobacter cloacae in the non Se-reducing strain E. coli S17-1 activates selenate reductase activity and the ability to precipitate Se(0) particles. Se(VI) reduction by E. coli S17-1 containing the fnr gene occurred at similar rates as E. cloacae, with first order reaction constants of k = 2.07 × 10-2 hour-1 and k = 3.36 × 10-2 hour-1 respectively, and resulted in the precipitation of elemental selenium particles with similar morphologies and identical short range atomic order. Our findings indicate that Se(0) biomineral formation by facultative anaerobes is activated by oxygen sensing transcription factors, and occurs under suboxic conditions.