Mobilization of selenite by Ralstonia metallidurans CH34

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soi l bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 i s reported now to resist up to 6 mM selenite and to reduce selenite to elem ental red selenium as shown by extended X-ray absorption fine-structure ana lysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture condi tions, the medium can be completely depleted of selenite. Selenium accumula tes essentially in the cytoplasm as judged from electron microscopy and ene rgy dispersive X-ray analysis. Elemental selenium, highly insoluble, repres ents a nontoxic storage form for the bacterium. The ability of R. metallidu rans CH34 to reduce large amounts of selenite may be of interest for biorem ediation processes targeting selenite-polluted sites.