The significance of iron(III) reducing bacteria in uranium(VI) bioremediation and energy production by sediment fuel cells
Dissimilatory Fe(III) reduction is one of the most significant metabolisms in sedimentary environments. Molecular and geochemical studies conducted on uranium contaminated sediments suggested that Fe(III) reducing bacteria could be stimulated to reduce U(VI) in uranium contaminated subsurface sediments. This is particularly significant because U(VI) is highly soluble, and therefore mobile, in most groundwaters whereas the reduced form of uranium, U(IV), is generally insoluble and precipitates from most groundwaters. Therefore, stimulating microbial reduction of U(VI) could potentially stop the spread of uranium contamination in the subsurface and, if the bioremediation process is engineered properly, concentrate uranium into a discrete zone for subsequent recovery. The anaerobic electrode of sediment fuel cells is another sedimentary environment where dissimilatory Fe(III) reducing bacteria predominate. Molecular and culturing studies have shown that dissimilatory Fe(III) reducing microorganisms are directly involved in electricity production by sediment fuel cells. These findings should help with the development and optimization of several environmentally relevant tools; i.e. microbial fuel cells that convert waste to useable energy forms. Further evaluation of the dissimilatory Fe(III) reducing microbial communities associated with these two important sedimentary environments suggested that a specific group of organisms, the Geobacteraceae, are primarily responsible for uranium removal from subsurface sediments and electron transfer to an electrode. In fact, two organisms, strains A1 and A2, were recovered from the surface of an electrode and are able to quantitatively transfer electrons available from the complete oxidation of organic acids to an electrode surface. A detailed evaluation of pure cultures of Geobaceraceae species indicated that the Geobacteraceae are a phylogenetically and physiologically distinct family within the δ-subdivision of Proteobacteria. This unique physiology may allow Geobacteraceae species to be most competitive in these sedimentary environments. Another family of dissimilatory metal reducing microorganisms, the Desulfobulbaceae, were also found to be associated with the current-harvesting anodes of marine sediment fuel cells. Further evaluation of a member of this family, Desulfobulbus propionicus, indicated that this organism is also capable of dissimilatory Fe(III) reduction and is able to directly transfer electrons to an electrode. Thus, Desulfobulbaceae species may also contribute to energy production in marine sediment fuel cells.
0775: Environmental engineering