Isolation of a mercuric chloride-tolerant bacterium and uptake of mercury by the bacterium

Summary

A mercuric chloride-tolerant bacterium was isolated from activated sludge and the bacterium was identified as Pseudomonas oleovorans.

The bacterium is tolerant up to 350 ppm Hg²⁺, 100 ppm Cd²⁺, 40 ppm cr⁶⁺, and 1000 ppm Cu²⁺. Observation by scanning electron microscope of cells growing with mercury shows a less rigid structure of the cell surface than in the case of controls, while observation by transmission electron microscope shows many electron-dense granules in the cytoplasm of cells growing with mercury. By chemical analysis, about 80% of mercury taken up by the cells was found in the cytoplasm, and about 20% in the cell envelope fraction, of the resting cells used. Mercury was found in the supernatant fluid, but not in the microsomal fraction.

Further detailed experiments for mercury distribution in the cells show that it is concentrated in the nucleic acid fraction of the supernatant fluid. In the insoluble fraction, mercury was found mainly in the polyphosphate-polysaccharide, mucopeptide, and lipopolysaccharide-polysaccharide fractions. In the case of the growing cells used, about 20% of the mercury was found in the cytoplasm and 80% in the insoluble fraction.