Bacterial strain UFZ B 490, which was isolated from a uranium dump and is closely related to Desulfovibrio vulgaris oxamicus(T) (DSM 1925(T)), is able to detoxify U(VI) in aqueous media. In experiments reported here, U(VI) was used as an electron acceptor and lactate as electron donor. The reduction of soluble U(VI) to solid U(IV) (uraninite) did not provide energy for growth of strain UFZ B 490. However, the isolate is able to grow when supplied with nitrate as sole electron acceptor and nitrogen source, using lactate as a source of carbon and energy. In comparative studies, the strains Desulfovibrio vulgaris oxamicus(T) (DSM 1925(T)) and Desulfovibrio vulgaris vulgaris(T) (DSM 644(T)), as well as the isolate, all utilized 0.6 mol lactate per mol U(VI) reduced. Strains UFZ B 490 and Desulfovibrio vulgaris oxamicus(T) (DSM 1925(T)) were found to consume 2.4 mol lactate per mol nitrate reduced, but Desulfovibrio vulgaris vulgaris(T) (DSM 644(T)) did not display dissimilatory nitrate reduction. In further experiments it was found that strain UFZ B 490 preferred sulfate as electron acceptor in the presence of both sulfate and nitrate, irrespective of whether it had been precultivated on sulfate or nitrate.