Mn II Oxidizing Activity of Pseudomonas

There has been an increasing interest in the application of Mn(II) oxidizing microbes for Mn(II) contaminating waste water treatment, as well as biogenic Mn oxides for remediation of a number of toxic metals. This study focuses on the Mn(II) oxidizing bacteria involved in the massive Mn oxide deposit formation at the Sambe hot spring in Japan. Through culture enrichment, Pseudomonas sp. strain MM1 was isolated as the predominant Mn(II) oxidizing bacterium from the site. The biogenic Mn oxide produced was identified as poorly-crystalline birnessite with a specific surface area of 90 m² g⁻¹. Strain MM1 effectively oxidized Mn(II) during its stationary phase, successfully reducing initial concentrations of up to 1.0 mmol·dm⁻³ back within the effluent standards of the Japanese Ministry of Environment. Growth of strain MM1 was heterotrophic, and Mn(II) was not the sole electron donor. Nano-sized Mn oxide particles formed by strain MM1 were observed to aggregate into larger minerals, with cells becoming encrusted within the oxides. Findings highlight the significant role of strain MM1 in producing Mn oxide deposits, indicating potential for bioremediation applications involving toxic metals.