Existence of an iron-oxidizing Bacterium acidithiobacillus ferrooxidans resistant to organomercurial compounds

Acidithiobacillus ferrooxidans MON-1 which is highly resistant to Hg ²⁺ could grow in a ferrous sulfate medium (pH 2.5) with 0.1 μM p-chloromercuribenzoic acid (PCMB) with a lag time of 2 d. In contrast, A. ferrooxidans AP19-3 which is sensitive to Hg²⁺ did not grow in the medium. Nine strains of A. ferrooxidans, including seven strains of the American Type Culture Collection grew in the medium with a lag time ranging from 5 to 12 d. The resting cells of MON-1, which has NADPH-dependent mercuric reductase activity, could volatilize Hg⁰ when incubated in acidic water (pH3.0) containing 0.1 μM PCMB. However, the resting cells of AP19-3, which has a similar level of NADPH-dependent mercuric reductase activity compared with MON-1, did not volatilize Hg⁰ from the reaction mixture with 0.1 μM -e;e;PCMB. The activity level of the 11 strains of A. ferrooxidans to volatilize Hg⁰ from PCMB corresponded well with the level of growth inhibition by PCMB observed in the growth experiments. The resting cells of MON-1 volatilized Hg⁰ from phenylmercury acetate (PMA) and methylmercury chloride (MMC) as well as PCMB. The cytosol prepared from MON-1 could volatilize Hg⁰ from PCMB (0.015 nmol mg^-11), PMA (0.33 nmol rag^-1 h^-1) and MMC (0.005 nmol mg^-1 h^-1) in the presence of NADPH and β-mercaptoethanol.