Measurement of copper uptake in Saccharomyces cerevisiae using a Cu2+-selective electrode

Cadmium adsorption by E. coli with surface displayed CadR

CadR is a metal-binding protein first isolated from rhizobacteriumPseudomonas putida.

Effective display of metallothionein tandem repeats on the bioadsorption of cadmium ion

To increase the level of adsorption of heavy metal ions in surface-engineered yeasts, a yeast metallothionein (YMT) was tandemly fused and displayed by means of an alpha-agglutinin-based display system. The display of the YMT and its tandem repeats was examined by immunofluorescent labeling. The adsorption and recovery of Cd(2+) on the cell surface was increasingly enhanced with increasing number of tandem repeats. All Cd(2+)-binding sites in the YMT tandem repeats were suggested to be completely occupied. To investigate the relationship between cell-surface adsorption and protection against heavy metal ion toxicity, the tolerance of these surface-engineered yeasts to Cd(2+) was examined by growing in Cd(2+)-containing liquid medium. The rate of growth was found to be dependent on the number of displayed tandem repeats of YMT. These results suggest that the characteristics of surface-engineered yeasts as a bioadsorbent were dependent on the ability of the displayed proteins to bind metal ions, and the adsorption of heavy metal ions on the cell surface plays a major role in the ability of the cells to resist the toxic effects of metal ions.

Influence of copper on proton efflux from Saccharomyces cerevisiae and the protective effect of calcium and magnesium

The inhibitory effect of Cu on glucose-dependent H+ efflux from Saccharomyces cerevisiae was manifest at low (micromolar) concentrations, with the time period between the addition of glucose and commencement of H+ efflux, H+ efflux rate and duration all being affected with increasing Cu concentration (5-100 microM). Ca, at a concentration of 0.5 mM, completely removed the inhibitory effect of Cu at concentrations up to 50 microM and considerably reduced it at higher concentrations (up to 150 microM). Mg exhibited a similar but weaker protective effect against the influence of Cu. The protective effect of Ca against 50 microM Cu was evident at low Ca concentrations (2.5-5 microM), whereas Mg was effective at > or = 50 microM. In order to prevent the inhibitory effect of Cu, it was necessary to add Ca or Mg to the cell suspension before Cu addition. It is concluded that the protective effect of Ca and Mg is mediated by competitive and stabilizing interactions at the cell surface as well as physiological functions of Ca and Mg.