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Applied and Environmental Microbiology, March 2008, p. 1527-1534, Vol. 74, No. 5
0099-2240/08/$08.00+0     doi:10.1128/AEM.01240-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Direct Identification of a Bacterial Manganese(II) Oxidase, the Multicopper Oxidase MnxG, from Spores of Several Different Marine Bacillus Species ^,

Gregory J. Dick,^1, Justin W. Torpey,² Terry J. Beveridge,^3, and Bradley M. Tebo^1*

Marine Biology Research Division, Scripps Institution of Oceanography, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0202,¹ Biomolecular Mass Spectrometry Facility, Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093-0378,² Department of Molecular and Cellular Biology, College of Biological Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada³

Received 4 June 2007/ Accepted 20 December 2007

Microorganisms catalyze the formation of naturally occurring Mn oxides, but little is known about the biochemical mechanisms of this important biogeochemical process. We used tandem mass spectrometry to directly analyze the Mn(II)-oxidizing enzyme from marine Bacillus spores, identified as an Mn oxide band with an in-gel activity assay. Nine distinct peptides recovered from the Mn oxide band of two Bacillus species were unique to the multicopper oxidase MnxG, and one peptide was from the small hydrophobic protein MnxF. No other proteins were detected in the Mn oxide band, indicating that MnxG (or a MnxF/G complex) directly catalyzes biogenic Mn oxide formation. The Mn(II) oxidase was partially purified and found to be resistant to many proteases and active even at high concentrations of sodium dodecyl sulfate. Comparative analysis of the genes involved in Mn(II) oxidation from three diverse Bacillus species revealed a complement of conserved Cu-binding regions not present in well-characterized multicopper oxidases. Our results provide the first direct identification of a bacterial enzyme that catalyzes Mn(II) oxidation and suggest that MnxG catalyzes two sequential one-electron oxidations from Mn(II) to Mn(III) and from Mn(III) to Mn(IV), a novel type of reaction for a multicopper oxidase.

Published ahead of print on 28 December 2007.

Supplemental material for this article may be found at http://aem.asm.org/.

Present address: Department of Geological Sciences, University of Michigan, 1100 N. University Avenue, Ann Arbor, MI 48109-1005.

Deceased 10 September 2007.

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