Bacteria from uranium mining waste pile: interactions with U(VI)

This study is our first effort to obtain more information on the effects of microbial activities on the mobilization/immobilization of radionuclides in geological environments. We used aerobic and anaerobic strains of bacteria to quantify interactions with U(VI). The quantification of bioaccumulation by two strains of Thiobacillus ferrooxidans has shown a slightly higher capability to accumulate U for T. ferrooxidans ATCC 33020, isolated from a uranium mine, than for the type strain T. ferrooxidans ATCC 23270 T, recovered from a coal mine. The amount of accumulated uranium increased for both strains when the pH was increased from 1.5 to 4.0. Extraction studies with EDTA showed that only a small part of the accumulated uranium is adsorbed on the surface of the cell walls whereas the main part is probably taken up by the cells. We also examined the U(VI) reduction of a sulfate-reducing bacterial strain ( Desulfovibrio desulfuricans DSM 642 T). In addition, we have studied one sulfate-reducing culture from a uranium mining waste pile (JG 1). Kinetic studies with D. desulfuricans have shown that most of U(VI) is reduced during the first 24 h. The yield of this microbial reduction depends strongly on the pH and increases from 10.3 to 99.2% when the pH is increased from 3.1 to 6.2. In nature D. desulfuricans strains occur in places where the pH is near neutral.