Manganese-oxidizing microbes and biogenic manganese oxides: characterization, Mn(II) oxidation mechanism and environmental relevance

Manganese oxides are the strongest natural oxidants in our environments aside from oxygen. Most natural manganese oxides are produced through the Mn(II) oxidation process driven by microbes. Biogenic manganese oxides (BioMnOx) are usually amorphous and rich in defects and possess large surface areas, resulting in high oxidative reactivity and strong absorption capacity for many emerging pollutants. Up to date, numerous of Mn(II) oxidation microbes (MnOM) have been isolated and characterized. Both directly enzymatic or indirectly abiotic Mn(II) oxidation processes were found in MnOM, but a systemic summarization about the Mn(II) oxidation mechanism is still lack. Moreover, the differentiation among BioMnOx produced by different MnOM needs to compare. As a potential oxidant and catalyst for pollutants removal, the role of BioMnOx in environmental remediation is also rarely mentioned. In this review, we focus on the Mn(II) oxidation process mediated by different MnOM, including their Mn(II) oxidation characterization and putative mechanism, as well as characterization of BioMnOx, and BioMnOx-related environmental remediation processes.