Abstract
Remediation of former uranium mining sites represents one of the biggest challenges worldwide that have to be solved in this century. During the last years, the search of alternative strategies involving environmentally sustainable treatments has started. Bioremediation, the use of microorganisms to clean up polluted sites in the environment, is considered one the best alternative. By means of culture-dependent methods, we isolated an indigenous yeast strain, KS5 (Rhodosporidium toruloides), directly from the flooding water of a former uranium mining site and investigated its interactions with uranium. Our results highlight distinct adaptive mechanisms towards high uranium concentrations on the one hand, and complex interaction mechanisms on the other. The cells of the strain KS5 exhibit high a uranium tolerance, being able to grow at 6 mM, and also a high ability to accumulate this radionuclide (350 mg uranium/g dry biomass, 48 h). The removal of uranium by KS5 displays a temperature- and cell viability-dependent process, indicating that metabolic activity could be involved. By STEM (scanning transmission electron microscopy) investigations, we observed that uranium was removed by two mechanisms, active bioaccumulation and inactive biosorption. This study highlights the potential of KS5 as a representative of indigenous species within the flooding water of a former uranium mine, which may play a key role in bioremediation of uranium contaminated sites.
Highlights
Our present study describes the interaction mechanisms of KS5 with uranium(VI) and its tolerance to selected heavy metals
Uranium removal studies and Transmission electron microscopy (TEM) analyses revealed that the cells of the strain interact with uranium through a temperature-dependent process
For yeast cells incubated at 30 ̊C, intracellular uranium accumulates as needle-like structures were detected in the cytoplasm and within lipid-granules, which might be a consequence of different detoxification mechanisms
Summary
Heavy metal pollution of the environment is one of the biggest problems today due to its great impact on the surface and groundwater, and even in the catchment areas of drinking water. Previous studies showed that uranium mainly occurs in the bulk solution as highly soluble UO2SO4-species within the flooding water of the former uranium mine [9] Besides abiotic factors such as pH, redox potential, dissolved organic and inorganic ligands, and the presence of solid particulates [5,10,11], biological processes could have a significant impact on the migration of radionuclides. It seems to be important to consider microorganisms from ecological niches, like the former uranium mining site Konigstein, for the use in metal bioremediation approaches, since conventional technologies, such as chemical precipitation and ion exchange, are cost-intensive and often inefficient for metals at low concentrations [27,28,29]. The results of our investigations provide new insights on the interaction of indigenous yeast cells with uranium, and a possible use of microbial cells for in situ bioremediation
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