KINETIC COEFFICIENTS FOR SIMULTANEOUS REDUCTION OF SULFATE AND URANIUM BY DESULFOVIBRIO-DESULFURICANS

Previously it was demonstrated that bacteria are capable of transformi ng soluble uranyl ion, U(VI), to insoluble uraninite, U(IV); however, the rate for this transformation has not been determined. We report th e kinetic coefficients for Desulfovibrio desulfuricans DSM 1924 grown in a continuous-flow chemostat where pyruvate was the electron donor a nd sulfate was the electron acceptor. The medium was supplemented with 1 mM uranyl nitrate, and the chemostat flow rate ranged from 1.12 ml/ h to 4.75 ml/h with incubation at 28 degrees C. The maximum rate of py ruvate utilization (k) was determined to be 4.7 days(-1), while the ha lf-velocity constant (K-s) was 127 mg/l. The yield coefficient (Y) of cells per mole of pyruvate oxidized was calculated to be 0.021 g, whil e the endogenous decay coefficient (k(d)) was determined to be 0.072 d ays(-1). More than 90% of U(VI) was transformed to U(VI) in the chemos tat under the conditions employed.