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Applied and Environmental Microbiology, October 2006, p. 6467-6473, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.00417-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Manganese(IV) Oxide Production by Acremonium sp. Strain KR21-2 and Extracellular Mn(II) Oxidase Activity

Naoyuki Miyata,1* Yukinori Tani,1 Kanako Maruo,2 Hiroshi Tsuno,3,{dagger} Masahiro Sakata,1 and Keisuke Iwahori1

Institute for Environmental Sciences,1 Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka 422-8526, Japan,2 National Institute of Advanced Industrial Science and Technology, Tsukuba 305-8569, Japan3

Received 20 February 2006/ Accepted 19 July 2006

Ascomycetes that can deposit Mn(III, IV) oxides are widespread in aquatic and soil environments, yet the mechanism(s) involved in Mn oxide deposition remains unclear. A Mn(II)-oxidizing ascomycete, Acremonium sp. strain KR21-2, produced a Mn oxide phase with filamentous nanostructures. X-ray absorption near-edge structure (XANES) spectroscopy showed that the Mn phase was primarily Mn(IV). We purified to homogeneity a laccase-like enzyme with Mn(II) oxidase activity from cultures of strain KR21-2. The purified enzyme oxidized Mn(II) to yield suspended Mn particles; XANES spectra indicated that Mn(II) had been converted to Mn(IV). The pH optimum for Mn(II) oxidation was 7.0, and the apparent half-saturation constant was 0.20 mM. The enzyme oxidized ABTS [2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)] (pH optimum, 5.5; Km, 1.2 mM) and contained two copper atoms per molecule. Moreover, the N-terminal amino acid sequence (residues 3 to 25) was 61% identical with the corresponding sequence of an Acremonium polyphenol oxidase and 57% identical with that of a Myrothecium bilirubin oxidase. These results provide the first evidence that a fungal multicopper oxidase can convert Mn(II) to Mn(IV) oxide. The present study reinforces the notion of the contribution of multicopper oxidase to microbially mediated precipitation of Mn oxides and suggests that Acremonium sp. strain KR21-2 is a good model for understanding the oxidation of Mn in diverse ascomycetes.

* Corresponding author. Mailing address: Institute for Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga, Shizuoka 422-8526, Japan. Phone: 8154-264-5649. Fax: 8154-264-5594. E-mail: miyatan{at}smail.u-shizuoka-ken.ac.jp.

{dagger} Present address: Faculty of Education and Human Sciences, Yokohama National University, 79-2 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan.

Applied and Environmental Microbiology, October 2006, p. 6467-6473, Vol. 72, No. 10
0099-2240/06/$08.00+0     doi:10.1128/AEM.00417-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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