Mobilization of Selenite by Ralstonia metallidurans CH34

Abstract

Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a soil bacterium characteristic of metal-contaminated biotopes, as it is able to grow in the presence of a variety of heavy metals. R. metallidurans CH34 is reported now to resist up to 6 mM selenite and to reduce selenite to elemental red selenium as shown by extended X-ray absorption fine-structure analysis. Growth kinetics analysis suggests an adaptation of the cells to the selenite stress during the lag-phase period. Depending on the culture conditions, the medium can be completely depleted of selenite. Selenium accumulates essentially in the cytoplasm as judged from electron microscopy and energy-dispersive X-ray analysis. Elemental selenium, highly insoluble, represents a nontoxic storage form for the bacterium. The ability of R. metallidurans CH34 to reduce large amounts of selenite may be of interest for bioremediation processes targeting selenite-polluted sites.In aerated environments, selenium can exist in several redox forms, including the elemental form, Se(0), which is a solid, and the oxidized forms, selenite (SeO 3 2Ϫ ) and selenate (SeO 4 2Ϫ ), which are bioavailable, mobile, and toxic for many organisms (5). Selenium is widely distributed in virtually all materials of the earth's crust, but accumulation of toxic compounds of selenium can also have an anthropogenic source. Selenium and its derivatives are widely used in industrial products, and the problem of selenium accumulation remains in mind after the ecological disaster of Kesterson National Wildlife Refuge, in California, due to agricultural drainage released in the Kesterson Reservoir (19). Since microorganisms are involved in the geochemical cycle of selenium, soil bacteria may thus be used in bioremediation processes. Some of them are able to resist high concentrations of a variety of metals and oxyanions (16), and the reduction of selenite to selenium by the common aerobic soil bacterium Bacillus subtilis (10) or the phototrophic purple nonsulfur bacterium Rhodospirillum rubrum (12) has been reported. The accumulation of selenium by Rhodobacter sphaeroides has been also reported very recently (23).Ralstonia metallidurans CH34 (formerly Alcaligenes eutrophus CH34) is a microorganism characteristic of metal-contaminated biotopes (14 . Resistance is due mainly to plasmid-mediated efflux followed by postefflux events such as bioprecipitation or biological sequestration (1, 7). In this report, the ability of R. metallidurans CH34 to resist also selenite is described for the first time. The physiological and morphological changes resulting from the presence of selenite in the culture medium were studied by using direct chemical assay for selenite, electron microscopy, and electron-dispersive X-ray analysis. The speciation of selenium was determined by X-ray absorption spectroscopy techniques. MATERIALS AND METHODSStrain and growth media. R. metallidurans CH34 was grown under aerobic conditions at 29°C in the minimal mineral medium described in reference 15. As this medium ...

Similarities between the Abiotic Reduction of Selenite with Glutathione and the Dissimilatory Reaction Mediated by Rhodospirillum rubrum and Escherichia coli

“…Consistent with the involvement of glutathione in the dissimilatory reduction of selenite, various proteobacteria belonging to these groups have been shown to tolerate millimolar levels of selenite (6,12,19,20). In contrast, a broad survey of selenite tolerance in bacteria (63 species) demonstrated that most species (81%) are not able to grow in the presence of 0.2 mM selenite (25).…”

“…6,12,19,20). The threshold of selenite concentration that the cells are able to reduce may reflect, at least in part, the large requirement of oxidative stress enzymes for this process.…”

“…The final yield of Se°was relatively low (45-80%) compared with that of the bacterially mediated reaction (see, e.g. 6,18,19) and was in most cases only slightly improved by increasing the ratio of GSH to selenite (Fig. 4B).…”

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides – 1. Microbial Processes and Mechanisms Affecting Bioremediation of Metal Contamination and Influencing Metal Toxicity and Transport

“…This strain is a good candidate for the accelerated bioremediation of systems contaminated by high levels of cadmium Sharma et al 2000 Subsurface sediment Uranium Stimulation of dissimilatory metal reduction activity of an enrichment of microorganisms closely related to Pseudomonas and Desulfosporisinus sp. which promote the reductive precipitation of uranium Nevin et al 2003 Selenite polluted site Selenium Ralstonia metallidurans CH34 can reduce selenite to elemental red selenium, that is highly insoluble Roux et al 2001 Subsurface sediment Subsurface environments Uranium Biofilm of the sulfate reducing bacterium Desulfovibrio desulfuricans attached to hematite (a-Fe 2 O 3 ) surface can accumulates both U(VI) and U(IV) and thus can limit the transport of uranium in subsurface environments Neal et al 2004 substances. Research in bioremediation is now opening the virtually infinite possibilities inherent in enzymatic systems.…”

Introduction to a special Festschrift issue celebrating the microbiology of Cupriavidus metallidurans strain CH34

“…Firstly, this unusual multiple toxic metal ion-resistant bacterium has been a model for how microbes handle such toxic metal (loids) from the time of its first isolation (Mergeay et al 1978(Mergeay et al , 1985. Moreover, it continues to be a useful model, as seen in this series of reports as well as in any search of the literature, used for an expanding range of interests from metal response physiology (Nies et al 1990(Nies et al , 1989Nies 2000;Roux et al 2001;Sendra et al 2006) and basic molecular genetics (Lejeune et al 1983), to genomics (the organism is unusual in having two chromosomes plus two large plasmids; Mergeay et al 2003), microbial ecology (Vander Auwera, this series), to applications in environmental biotechnology (Diels, this series) and even in space research (Leys, this series).…”