TEM investigation of U6+ and Re7+ reduction by Desulfovibrio desulfuricans, a sulfate-reducing bacterium

Uranium and its fission product Tc in aerobic environment will be in the forms of UO22+ and TcO4-. Reduced forms of tetravalent U and Tc are sparingly soluble. As determined by transmission electron microscopy, the reduction of uranyl acetate by immobilized cells of Desulfovibrio desulfuricans results in the production of black uraninite nanocrystals precipitated outside the cell. Some nanocrystals are associated with outer membranes of the cell as revealed from cross sections of these metabolic active sulfate-reducing bacteria. The nanocrystals have an average diameter of 5 nm and have anhedral shape. The reduction of Re7+ by cells of Desulfovibrio desulfuricans is fast in media containing H2 an electron donor, and slow in media containing lactic acid. It is proposed that the cytochrome in these cells has an important role in the reduction of uranyl and Re7+ is (a chemical analogue for Tc7+) through transferring an electron from molecular hydrogen or lactic acid to the oxyions of UO22+ and TcO4-