|
The effect of metallothionein expression on the metal resistance and removal by recombinant Saccharomyces cerevisiae containing the plasmid pJW9 was investigated. The recombinant strain S. cerevisiae BZ-pJ was constructed by transforming the host strain S. cerevisiae BZ31-1-7Ba with the gene coding for a metal-binding protein, metallothionein. Introduction of the MT gene yielded an increase in the minimum inhibitory concentration(MIC) of copper more than three times compared with the host strain. The minimum inhibitory concentrations of Cr", Zn2+, and Pb" were not different for the two strains. The recombinant yeast grown in a medium containing 8mM CUSO, was able to remove copper with a capacity of 18.9mg Cu+2/g dry cell. In a mixture of copper and zinc, the presence of copper relieved the toxic effects caused by zinc, resulting in an enhancement of the final cell density and the specific growth rate of the recombinant yeast. The capability to remove copper by the recombinant yeast was linearly proportional to the copper concentrations in the medium. The efficiency of copper removal was rather constant regardless of the initial copper concentrations. The specific removal of zinc was dependent on the zinc concentrations in media, though, and such a dependence was not so pronounced as the concentration of copper.
|