TEM Investigation of U6+ and Re7+ Reduction by Desulfovibrio desulfuricans, a Sulfate-Reducing Bacterium

Abstract

Uranium and its fission product Tc in aerobic environment will be in the forms of UO{sub 2}{sup 2+} and TcO{sub 4}{sup {minus}}. 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 Re{sup 7+} by cells of Desulfovibrio desulfuricans is fast in media containing H{sub 2} 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 Re{sup 7+} is (a chemical analogue for Tc{sup 7+}) through transferring an electron from molecular hydrogen or lactic acid to the oxyions of UO{sub 2}{sup 2+} and TcO{sub 4}{sup {minus}}.