Mn(Ⅱ) Oxidation Of A Deep Sea Manganese-Oxidizing Brachybacterium Sp. Mn32 And Sorption Of Zn(Ⅱ),Ni(Ⅱ) By Biogenic Mn Oxides

Manganese-oxidizing microorganisms have been found in soil,fresh water,deep sea and sediment.They are able to oxidize soluble Mn²⁺ into insoluble Mn oxides and the biogenic Mn oxides could adsorb heavy metals.Thus,Manganese-oxidizing microorganisms are very useful in treatment of heavy metal-contaminated water.The ocean gram positive Manganese-oxidizing bacterium Brachybacterium sp. Mn32 was isolated from Pacific Ocean deep sea Mn-Co nodule.It has high Mn²⁺ tolerance and can oxidize Mn²⁺ efficiently.In this study,oxidation and removing of Mn²⁺ by Mn32 was determined,and preliminary oxidation mechanism was also studied.The heavy metal ion(Zn²⁺ and Ni²⁺) sorption characteristic of biogenic Mn oxides produced by Mn32 was investigated and compared with those of abiogenic Mn oxides(commercial MnO₂ and chemical synthetic MnO₂).The results indicated that Mn32 had high Mn²⁺ oxidation and removing abilities. Nearly 100%of 0.2mmol/L Mn²⁺ in 150mL medium has been oxidized and removed by Mn32 in a period of 5 days.Mn32 removed Mn²⁺ by two ways,1) Mn32 produced oxidase to transform Mn²⁺ to solid biogenic Mn oxides,2) The biogenic Mn oxides can still adsorbed more Mn²⁺ from the solution.In this study,heavy metal(Zn²⁺ and Ni²⁺) sorption abilities of biogenic Mn oxides produced by Mn32 and abiogenic Mn oxides(commercial and chemical synthetic MnO₂) was determined.The adsorption molar ratio of biogenic Mn oxides were 0.206 mol Zn/mol Mn and 0.132 mol Ni/mol Mn;The adsorption molar ratio of commercial MnO₂ were 0.059mol Zn/mol Mn and 0.06 mol Ni/mol Mn;The adsorption molar ratio of chemical synthetic MnO₂ were 0.064 mol Zn/mol Mn and 0.063mol Ni/mol Mn.The adsorption capacity of the biogenic Mn oxides is 2-3 times higher than that of the commercial or chemical synthetic MnO₂.The structures of the 3 kinds of Mn oxides were observed using scan electron microscope.It showed that particles of the biogenic Mn oxides were more regular than those of commercial and chemical synthetic MnO₂.X-ray diffraction was performed to analyze crystal structures of 3 kinds of Mn oxides.It was found that the crystal types of the 3 kinds of Mn oxides are different.The typical crystal structure and the biogenic MnO₂ type are the very important reasons for the high adsorption ability of Mn32.This study provides the valuable application of a manganese-oxidizing bacterium in heavy metal bioremediation and the basic knowledge of the manganese oxidation machanisms.