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

Long-term batch experiments in an artificial groundwater medium indicated t hat microbial reduction of synthetic, high-surface-area goethite and lepido crocite by Shewanella putrefaciens 200 can act to immobilize surface-associ ated 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, additi onal Zn immobilization may result from incorporation into as yet unidentifi ed biogenic minerals or into a more crystalline goethite. Experiments with an oxide mixture primarily composed of lepidocrocite resulted in the produc tion of magnetite, biphasic immobilization of Zn, and an enhanced overall d egree of Zn immobilization. When NO3- was present as an alternate electron acceptor, microbial production of Fe(II) was inhibited, and the degree of Z n immobilization was subsequently reduced. These data indicate that (i) bio logically induced mineralization can play a key role in the cycling of trac e elements in natural systems, (ii) the nature of the oxide surface plays a n important role in biologically induced mineralization, and (iii) conditio ns associated with Fe(II) production are necessary for these processes to i mmobilize surface-bound Zn within these new mineral phases.