Saccharomyces cerevisiae quiescent cells: cadmium resistance and adaptive response

The budding yeast Saccharomyces cerevisiae is a widely used model organism to investigate the changes occurring in the eukaryotic cell and to predict its possible 'reaction' to different environmental factors. Recently it was also shown that these microorganisms possess another advantageous ability: to 'enter' into quiescent state (G(0)). Yeast G(0) cells have similar physiological characteristics to those of higher eukaryotes making them a better model for toxicology studies. As cadmium could affect severely human health, the main aim of the present study was to use Saccharomyces cerevisiae quiescent cells to investigate the resistance potential and corresponding adaptive response of eukaryotic cells to elevated cadmium concentrations. Both diploid and haploid yeast strains in logarithmic, quiescent and non-quiescent state were exposed to different concentrations of Cd(NO3)(2). The half-maximal inhibitory concentration (IC50) for all tested cell types was 100 mu mol/L Cd(NO3)(2). The deleterious effects of cadmium on intracellular macromolecule structures were analyzed through evaluating the levels of accumulated reactive oxygen species (ROS) and carbonylated proteins. The highest ROS concentration was measured in logarithmic cells: up to 50% versus about 8% in G(0) cells. Significant damage in protein molecules was observed in haploid cells where the protein carbonylation reached levels of 25 mu mol/mg. Studying the adaptive response to elevated Cd2+ concentrations revealed that quiescent and non-quiescent cells respond with increased expression of key elements from the antioxidant defense system: reduced glutathione, superoxide dismutase (SOD) and catalase. Furthermore, an additional SOD izoenzyme was detected when diploid and haploid cell populations were exposed to Cd2+.