Biotransformations of Chromium and Uranium back to Research
Hexavalent chromium (Cr(VI)) and hexavalent uranium (U(VI)) are the toxic and highly soluble forms of these elements and are of great concern as pollutants in the environment. When reduced to Cr(III) or U(IV) these elements are much less soluble and hence less toxic. Thus, hexavalent Cr and U reduction, particularly by bacteria, is being explored as a (bio)remediation strategy for these elements. However, for this to be effective Cr and U must be stable in their reduced forms. The Tebo lab is interested in the mechanisms of Cr and U reduction by bacteria, the properties and stability of the reduced forms of these elements, and the mechanisms by which they may be reoxidized. We have isolated a number of novel bacteria capable of growing with Cr(VI) and U(VI) as electron acceptors and are investigating their response to Cr(VI) and U(VI) exposure. The full genome sequence of one our organisms, Desulfotomaculum reducens MI-1, will be used to characterize the metabolic capabilities of this bacterium. Both Cr(III) and U(IV) (hydr)oxides may be oxidized by Mn oxides, suggesting that Mn(II)-oxidizing bacteria play an important role in the stability of these phases. We have shown that Mn(II)-oxidizing bacteria accelerate the oxidation of Cr(III) over that observed by synthetic or biogenic Mn oxides alone and we seek to understand the mechanism of catalysis and the possible role of Mn(II)-oxidizing bacteria in U(IV) oxidation.