Interactions of natural occurring eukaryotic microorganisms with uranium(VI)

Despite high uranium concentrations (up to 14 mg/L) and low pH (2.5 – 3.0) a high microbial diversity was detected by culture independent methods in the flooding water of the former uranium mine Königstein (Saxony, Germany). In this study we used culture dependent techniques for the isolation of eukaryotic microorganisms from the flooding water. It was possible to isolate different eukaryotic fungi with a glucose rich medium. The microbial isolates identified by 16S rDNA and 18S rDNA were tested for their uranium tolerance abilities by the determination of the minimal inhibitory concentration (MIC) on solid media. The results showed high tolerances of uranium (up to 6 mM) on solid agar plates. Based on these results isolate KS5 (Rhodosporidium toruloides) and one reference organism DSM 10134 (Rhodosporidium toruloides) were selected for further uranium interaction experiments. Uranium biosorption tests indicated that the cells of the strain KS5 and the reference DSM 10134 are able to remove high amounts of uranium ranging between 120 and 160 mg uranium/g dry biomass. To test the uranium tolerance quantitative in liquid media flow cytometry experiments with KS5 and DSM 10134 were done. These results showed a higher uranium tolerance of the isolate KS5 compared to the reference culture of DSM 10134 like the tolerance test on solid medium. Summarizing the results of this study indicate that eukaryotic microorganisms within a uranium-contaminated environment could play an important role in the bioremediation of radionuclides.