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Reduction and Immobilization of Molybdenum by Desulfovibrio desulfuricans

Sandia National Laboratories, Albuquerque, NM 87185;

Larry L. Barton

Univ. of New Mexico, Dep. of Biology, Albuquerque, NM 87131;

Bruce M. Thomson

Univ. of New Mexico, Dep. of Civil Eng., Albuquerque, NM 87131.

^* Corresponding author (mdtucke{at}sandia.gov).

ABSTRACT

The mobility of Mo in the environment is strongly dependent on its chemical oxidation state. Under oxidizing conditions, Mo occurs as highly soluble and mobile Mo(VI) and Mo(V) compounds. However, under reducing conditions Mo usually forms insoluble Mo(IV) phases. The objective of this study was to demonstrate the ability of the sulfate-reducing bacterium, Desulfovibrio desulfuricans, to reduce Mo(VI) to Mo(IV) in anaerobic environments. Molybdenum-VI was reduced to Mo(IV) by washed cells of D. desulfuricans suspended in bicarbonate buffer solution with either lactate or H₂ 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 [MoS_2(s)]. Molybdenum-VI reduction did not occur in the absence of an electron donor or in the presence of heat-killed cells of D. desulfuricans. Attempts to grow D. desulfuricans with Mo(VI) as the sole electron acceptor were unsuccessful. Direct chemical reduction of Mo(VI) by sulfide or by H₂ was also unsuccessful, even when heat-killed cells of D. desulfuricans were added to provide a potential catalytic surface for the nonenzymatic reaction. Desulfovibrio vulgaris reduced Mo(VI) to 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 organisms may be useful for removing soluble Mo from contaminated water.

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