Zinc immobilization and magnetite formation via ferric oxide reduction by Shewanella putrefaciens 200

Long-term batch experiments in an artificial groundwater medium indicated that microbial reduction of synthetic, high-surface-area goethite and lepidocrocite by Shewanella putrefaciens 200 can act to immobilize surface-associated zinc into a new mineral phase that is not soluble in 0.5 M HCl. While Zn was incorporated in siderite grains in experiments with goethite, additional Zn immobilization may result from incorporation into as yet unidentified biogenic minerals or into a more crystalline goethite. Experiments with an oxide mixture primarily composed of lepidocrocite resulted in the production of magnetite, biphasic immobilization of Zn, and an enhanced overall degree of Zn immobilization. When NO3- was present as an alternate electron acceptor, microbial production of Fe(II) was inhibited, and the degree of Zn immobilization was subsequently reduced. These data indicate that (i) biologically induced mineralization can play a key role in the cycling of trace elements in natural systems, (ii) the nature of the oxide surface plays an important role in biologically induced mineralization, and (iii) conditions associated with Fe(II) production are necessary for these processes to immobilize surface-bound Zn within these new mineral phases.