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Multicopper oxidase involvement in both Mn(II) and Mn(III) oxidation during bacterial formation of MnO(2).

ABSTRACT: Global cycling of environmental manganese requires catalysis by bacteria and fungi for MnO(2) formation, since abiotic Mn(II) oxidation is slow under ambient conditions. Genetic evidence from several bacteria indicates that multicopper oxidases (MCOs) are required for MnO(2) formation. However, MCOs catalyze one-electron oxidations, whereas the conversion of Mn(II) to MnO(2) is a two-electron process. Trapping experiments with pyrophosphate (PP), a Mn(III) chelator, have demonstrated that Mn(III) is an intermediate in Mn(II) oxidation when mediated by exosporium from the Mn-oxidizing bacterium Bacillus SG-1. The reaction of Mn(II) depends on O(2) and is inhibited by azide, consistent with MCO catalysis. We show that the subsequent conversion of Mn(III) to MnO(2) also depends on O(2) and is inhibited by azide. Thus, both oxidation steps appear to be MCO-mediated, likely by the same enzyme, which is indicated by genetic evidence to be the MnxG gene product. We propose a model of how the manganese oxidase active site may be organized to couple successive electron transfers to the formation of polynuclear Mn(IV) complexes as precursors to MnO(2) formation.

SUBMITTER: Soldatova AV

PROVIDER: S-EPMC3743667 | biostudies-literature | 2012 Dec

REPOSITORIES: biostudies-literature

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Multicopper oxidase involvement in both Mn(II) and Mn(III) oxidation during bacterial formation of MnO(2).

Soldatova Alexandra V AV Butterfield Cristina C Oyerinde Oyeyemi F OF Tebo Bradley M BM Spiro Thomas G TG

Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry 20120815 8

Global cycling of environmental manganese requires catalysis by bacteria and fungi for MnO(2) formation, since abiotic Mn(II) oxidation is slow under ambient conditions. Genetic evidence from several bacteria indicates that multicopper oxidases (MCOs) are required for MnO(2) formation. However, MCOs catalyze one-electron oxidations, whereas the conversion of Mn(II) to MnO(2) is a two-electron process. Trapping experiments with pyrophosphate (PP), a Mn(III) chelator, have demonstrated that Mn(III ...[more]

PMID: 22892957

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Project description:Redox-driven reactions involving Mn(II) species adsorbed at Mn(IV) oxide surfaces can release Mn(III) in the form of dissolved Mn(III)-ligand species in natural waters. Using pyrophosphate (PP) as a model ligand, we show that freezing accelerates and enhances Mn(III) formation in the form of Mn(III)-PP complexes. This freeze-promoted reaction is explained by the concentration of Mn(IV) oxides and solutes (Mn(II), Na+, and Cl-) into the minute fractions of liquid water locked between ice (micro)crystals - the Liquid Intergrain Boundary (LIB). Time-resolved freezing experiments at -20 °C showed that Mn(III) yields were greatest at low salt (NaCl) content. In contrast, high salt content promoted Mn(III) formation through chloride complexation, although yields became lower as the cryosalt mineral hydrohalite (NaCl·2H2O) dehydrated the LIB by drawing water into its structure. Consecutive freeze-thaw cycles also showed that dissolved Mn(III) concentrations increased within the very first few minutes of each freezing event. Because each thaw event released unreacted PP previously locked in ice, each sequential freeze-thaw cycle increased Mn(III) yields, until ∼80% of the Mn was converted to Mn(III). This was achieved after only seven cycles. Finally, temperature-resolved freezing experiments down to -50 °C showed that the LIB produced the greatest quantities of Mn(III) at -10 °C, where the volumes were greater. Reactivity was however sustained in ice formed below the eutectic (-21.3 °C), down to -50 °C. We suspect that this sustained reactivity was driven by persistent forms of supercooled water, such as Mn(IV) oxide-bound thin water films. By demonstrating the freeze-driven production of Mn(III) by comproportionation of dissolved Mn(II) and Mn(IV) oxide, this study highlights the potentially important roles these reactions could play in the production of pools of Mn(III) in natural water and sediments of mid- and high-latitudes environments exposed to freeze-thaw episodes.

Dataset Information

Multicopper oxidase involvement in both Mn(II) and Mn(III) oxidation during bacterial formation of MnO(2).

Publications

Multicopper oxidase involvement in both Mn(II) and Mn(III) oxidation during bacterial formation of MnO(2).

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