Date of Award
Doctor of Philosophy (PhD)
Ray E. Ferrell, Jr
This study examines the interaction between two genera of bacteria and the biochemical reduction of uranium. The bacteria studied are the obligate anaerobe, Desulfovibrio desulfuricans, and the facultative aerobe, Escherichia coli. Preliminary experiments established the pH, cell concentration, substrate concentration, and type of substrate that favored reduction of hexavalent uranium in aqueous solutions. Uranium reduction is most complete at pH 7 and 9, with cell concentrations of at least 33.5 mg/ml (dry cell weight). Whole cells of D. desulfuricans were found to reduce uranium in the presence of lactate and hydrogen whereas in E. coli, reduction was achieved only in the presence of glucose. When using glucose or lactate, complete reduction did not occur until the concentration reached 5 mM. Cell fractions of each organism, including soluble periplasmic material and insoluble membrane fractions were also evaluated for their ability to reduce uranium. In D. desulfuricans the uranium reductase activity resides in a soluble periplasmic component whereas in E. coli, the enzymatic activity is membrane bound. When cell-free fractions of D. desulfuricans were used, reduction was possible only in the presence of hydrogen, suggesting a loss of a lactate oxidizing enzyme during the fractionation. Cell fraction immobilization and uranium reductase activity was also considered. Whole cells of D. desulfuricans immobilized onto Biosep beads had a rapid loss of hexavalent uranium but was not complete. A cell-free extract of D. desulfuricans was immobilized onto sepharose gel with no loss of activity. The most effective reduction in D. desulfuricans was achieved using whole cells with lactate and cell extracts with hydrogen, initial uranium concentrations of 250 mg/L were reduced to 0.0 mg/L within 13 hours and uraninite precipitated. In experiments with E. coli, initial hexavalent uranium levels were 25.0 mg/L. Reduction to 6.0 mg/L occurred within 60 minutes. Precipitation of uraninite did not occur in 48 hours using E. coli. This information on the interaction of microorgansims and uranium has potential as a waste remediation technique and to explain the origin of uranium ore bodies in shallow hydrogeologic environments.
Clark, Boyce Lamont, "Reductive Precipitation of Uranium by Free and Immobilized Cells and Cell Fractions of Facultative and Anaerobic Bacteria." (1997). LSU Historical Dissertations and Theses. 6539.