REDUCTION AND IMMOBILIZATION OF MOLYBDENUM BY DESULFOVIBRIO-DESULFURICANS

The mobility of Mo in the environment is strongly dependent on its che mical oxidation state. Under oxidizing conditions, Mo occurs as highly soluble and mobile Mo(VI) and Mo(V) compounds. However, under reducin g conditions Mo usually forms insoluble Mo(IV) phases. The objective o f this study was to demonstrate the ability of the sulfate-reducing ba cterium, Desulfovibrio desulfuricans, to reduce Mo(VI) to Mo(IV) in an aerobic environments. Molybdenum-VI was reduced to Mo(IV) by washed ce lls of D. desulfuricans suspended in bicarbonate buffer solution with either lactate or H-2 as the electron donor and Mo(VI) as the electron acceptor. Molybdenum-VI reduction by D. desulfuricans in the presence of sulfide resulted in the extracellular precipitation of the mineral molybdenite [MoS2(s)]. Molybdenum-VI reduction did not occur in the a bsence of an electron donor or in the presence of heat-killed cells of D. desulfuricans. Attempts to grow D. desulfuricans with Mo(VI) as th e sole electron acceptor were unsuccessful. Direct chemical reduction of Mo(VI) by sulfide or by H-2 was also unsuccessful, even when heat-k illed cells of D. desulfuricans were added to provide a potential cata lytic surface for the nonenzymatic reaction. Desulfovibrio vulgaris re duced Mo(VI) Mo(IV) equally well. The results indicate that enzymatic reduction of Mo(VI) by sulfate-reducing bacteria may contribute to the accumulation of Mo(IV) in anaerobic environments and that these organ isms may be useful for removing soluble Mo from contaminated water.