title: Manganese(IV) oxide production by Acremonium sp. strain KR21-2 and extracellular Mn(II) oxidase activity.
abstract: 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.
authors.affiliation: Institute for Environmental Sciences, University of Shizuoka, 52-1 Yada, Suruga, Shizuoka 422-8526, Japan. miyatan@smail.u-shizuoka-ken.ac.jp
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Miyata
authors.forename: Yukinori
authors.initials: Y
authors.lastname: Tani
authors.forename: Kanako
authors.initials: K
authors.lastname: Maruo
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tsuno
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sakata
authors.forename: Keisuke
authors.initials: K
authors.lastname: Iwahori
mesh_terms: D000164:Acremonium / Q000201:enzymology / Q000378:metabolism*; D001203:Ascomycota; D017895:Manganese Compounds / Q000378:metabolism*; D010084:Oxidation-Reduction; D010087:Oxides / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism*
chemical_list: D017895:Manganese Compounds; D010087:Oxides; C027424:manganese oxide; D010088:Oxidoreductases