Toxic Effects of Hg^<2+> to a Hg^<2+>-Resistant Pseudomonas in the Presence of Halide Ions

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A Hg^<2+>-resistant Pseudomonas which can utilize glycine as a sole carbon and nitrogen source was isolated from a municipal sewage treatment plant, and the toxicity of Hg^<2+> in the presence of halide ions was examined. In glycine medium without halide ions, bacterial growth was scarcely influenced even at an initial Hg^<2+> concentration of 25 μM. The viable cell count decreased when adsorbed Hg^<2+>was more than 300 μmol・g-cell^<-1>. The toxicity of Hg^<2+> was enhanced when the halide ion concentration was such that the [HgX_2]^0 complex (X=Br^- or I^-) in the solution became dominant. In the presence of [HgBr_2]^0 complex, complete growth inhibition of unacclimatized cells was observed at 2-3 μM Hg^<2+>. A sudden decrease in the viable cell count was evident when adsorbed Hg^<2+> was more than 15 μmol・g-cell^<-1>. Growth of the isolate pre-incubated in glycine medium containing 25 μM Hg^<2+> (acclimatized cells) was also inhibited completely at 10 μM Hg^<2+> in the presence of Br^-. The adsorption and toxicity of Hg^<2+> decreased with increasing halide ion concentration in which [HgBr_3]^- or [HgBr_4]^<2-> complexes exist dominantly. These results indicate that toxicity of Hg^<2+> was enhanced by the formatio of [HgX_2]^0 complex and was not governed by the amount of Hg^<2+> adsorbed to the cells.
公益社団法人日本生物工学会の論文
1995-02-25