Metabolism of Metals and Metalloids by the Sulfate-Reducing Bacteria

The bacteria and archaea that reduce sulfate to sulfide can transform a variety of metal(loids). The latter include metalloids (As, Se and Te), transition metals (Au, Co, Cr, Fe, Hg, Mo, Mn, Ni, Pb, Pd, Pt, Re, Rh, Tc, V, and Zn), and actinides (Pu and U). The conversions are achieved via (1) use of metal-specific enzymes, (2) cometabolism, i.e., use of non-substrate-specific enzymes, (3) biomethylation, (4) inorganic precipitation, (5) oxidation-reduction reactions in the growth medium; or (6) oxidation/cathodic depolarization of the elemental form. Respective examples are (1) the respiration of arsenate by Desulfosporosinus auripigmenti; (2) reduction of selenate and selenite to elemental selenium by enzymes involved in sulfate respiration or assimilation; (3) methylation of mercury; (4) precipitation of zinc sulfide in the supernatant; (5) reaction of sulfide and selenite forming selenium sulfide (SeS2) in the supernatant; and (6) the anaerobic corrosion of iron. Some of these processes yield valuable commodities, e.g., the precipitation of gold by Desulfovibrio desulfuricans. The understanding of anaerobic corrosion can lead to the prevention of corrosion of pipelines. The formation of selenium nanoparticles has potential applications in the design of drug-delivery systems. The formation of insoluble precipitates facilitates the design of bioremediation technologies. While some metals, e.g., Fe, Co, Mo, Mn, Ni, Se, V and Zn, are essential nutrients for bacterial growth, this review focuses on detoxification processes and not on trace metal assimilation into cellular materials.