Mn(II)-Oxidizing Activity of <i>Pseudomonas</i> sp. Strain MM1 is Involved in the Formation of Massive Mn Sediments around Sambe Hot Springs in Japan

Abstract

There has been an increasing interest in the application of Mn(II) oxidizing microbes for Mn(II) containing waste water treatment, as well as biogenic Mn oxides for remediation of a number of toxic metals. Sambe hot spring in Shimane Prefecture, Japan is known for its Mn-rich spring water, and Mn oxide sediments are widely distributed over an area of 60m © 80m of this region. With an aim to find out Mn(II) oxidizing bacteria involved in this massive Mn(II) oxide deposit formation, culture enrichment was undertaken. Pseudomonas sp. strain MM1 was isolated as dominant Mn(II) oxidizing bacterium from the site. Biogenic Mn oxide formed by strain MM1 was shown to be poorly-crystalline birnessite, having the large specific surface area of 90m 2 ·g ¹1 . Mn(II) was readily oxidized by strain MM1 during the stationary phase and initial Mn(II) concentrations of up to 1.0mmol·dm ¹3 (55mg·dm ¹3 ) went well below the effluent standard of dissolved manganese (10mg·dm ¹3 ; set by Japanese Ministry of Environment). Strain MM1 grew heterotrophically and Mn(II) did not serve as the sole electron donor. Nano-sized (30­ 50nm) Mn oxide particles were produced by strain MM1, which later chained or aggregated to form larger Mn oxide minerals. Cells were observed eventually encrusted inside the Mn oxides. This study showed the important role of strain MM1 in the production of massive Mn oxide deposits at Sambe hot spring. The Mn(II) oxidizing ability of this strain is potentially applied for bioremediation of toxic metals. [doi:10.2320/matertrans.M-M2013825]