Oxidation of Co by Mn oxide has been investigated using abiotically synthesized Mn oxide. However, oxidation of Co by biogenic Mn oxide is not well known. In this study, we isolated a Mn-oxidizing bacterium (Pseudomonas sp.), designated as strain NGY-1, from stream water. Sorption experiments on Co were carried out using biogenic Mn oxide produced by strain NGY-1. Similar sorption experiments were also conducted using a synthetic analogue of δ-MnO2. Sorption of Co on δ-MnO2 was faster and stronger than that on biogenic Mn oxide, which was possibly due to their structural difference and/or the presence of bacterial cells in biogenic Mn oxide. X-ray absorption near-edge structure spectra clearly demonstrated that Co was oxidized from the divalent to the trivalent state on biogenic Mn and δ-MnO2. The oxidation property of both the biogenic Mn oxide and δ-MnO2 was stronger under circumneutral conditions than under acidic conditions. Linear combination fitting using divalent and trivalent Co reference materials suggested that ∼90% of Co was oxidized at pH ∼ 6, whereas ∼80% was oxidized at pH ∼ 3. Oxidation properties of the biogenic Mn oxide and δ-MnO2 were similar, but Co(II) oxidation by biogenic Mn oxide was slower than that by δ-MnO2. The difference of Co oxidation may be caused by the coexisting bacterial cells or structural differences in the Mn oxides. Supplemental materials are available for this article. Go to the publisher's online edition of Geomicrobiology Journal to view the supplemental file.
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