GEOC 77 |
| Samuel M. Webb1, John R. Bargar1, Gregory J. Dick2, Hope A. Johnson2, James K. McCarthy2, and B.M. Tebo2. (1) Stanford Synchrotron Radiation Laboratory, 2575 Sand Hill Road, Mail Stop 69, Menlo Park, CA 94025, (2) Marine Biology Research Division, Scripps Insitute of Oceanography, 9500 Gilman Dr, La Jolla, CA 92093 |
| Bacterial oxidation of Mn(II) is considered to be the dominant process in the formation of insoluble Mn(III,IV) oxides in the environment. However, very little is known regarding the Mn oxidation mechanism. Because Mn(II) oxidation is believed to be catalyzed by a multicopper oxidase, an enzyme that catalyzes one electron oxidations of their substrates, it is reasonable to assume that Mn(II) is oxidized to Mn(IV) via a Mn(III) intermediate. Here we show the existence of a Mn(III) intermediate in the oxidation of Mn(II) by several species of Bacillus spores, an α-proteobacterium, and Pseudomonas putida strain GB-1, as observed by the trapping of Mn(III) by pyrophosphate (PP). Addition of pyrophosphate to suspensions containing Mn(II) and the active enzyme from Bacillus sp. strain SG-1 results in the rapid production of a soluble Mn(III)-PP complex, which is eventually oxidized to Mn(IV). The production of Mn(III)-PP follows Michaelis-Menton kinetics. In SG-1 spores in which the putative oxidase gene has been inactivated through transposon mutagenesis, Mn(III) was not observed. In sum, our experiments provide further evidence that a multicopper oxidase is involved in Mn(II) oxidation and indicates that Mn undergoes two sequential one electron step processes in the oxidation from Mn(II) to Mn(IV), each of which are enzymatically catalyzed. The implications include a potential source of Mn(III) to the environment. |
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Microbially Mediated Manganese and Iron Oxidation in the Biosphere
1:30 PM-5:05 PM, Tuesday, March 30, 2004 Marriott -- Marquis NE, Oral
Division of Geochemistry |