Molecular biological study on the mechanism of a novel Fe^<2+>-dependent mercury reducing system of a mercury resistant iron-oxidizing bacterium

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Mercury is highly toxic for almost all organisms and thus, the removal of mercury from mercury polluted soil and wastewater is a worldwide problem. The final goal of this research project is volatilization and recovery of toxic mercury compounds from mercury polluted soil and wastewater using a highly mercury-resistant iron-oxidizing bacterium A.ferrooxidans strain MON-1. Acidithiobacillus ferrooxidans strain MON-1 is a highly mercury resistant strain that can grow in an iron medium (pH 2.5) with 20 μM mercuric chloride. Author has reported that strain MON-1 has a novel Fe^<2+>-dependent mercury volatilization enzyme system as well as a NADPH-dependent mercury reductase in the cells. In section 1, author analyzed for the first time the Fe^<2+>-dependent mercury volatilization system with TMPD as an electron donor for mercury volatilization reaction. It was found that strain MON-1 cells can volatilize Hg^0 with TMPD as an electron donor under anaerobic conditions and the activity was completely inhibited by 1 mM KCN, indicating that cytochrome c oxidase is involved in Hg^0 volatilization. Author isolated cytochrome c oxidase from MON-1 cells. A highly purified MON-1 cytochrome c oxidase could volatilize Hg^0 more rapidly when TMPD was used as electron donor compared with Fe^<2+>.There have been no reports on A.ferrooxidans strains resistant to organomercurial compounds probably because there has been no report on the organomercurial lyase gene (merB) in the bacterium. In section 2, author shows for the first time that the resting cells and the cytosol from strain MON-1, the most resistant to the organomercurial compounds among the 11 strains of A.ferrooxidans tested, had organomercurial lyase-like activity which catalyzed the volatilization of Hg^0 from the reaction mixture in the presence of NADPH, β-mercaptoethanol and the intrinsic mercuric reductase.