Response of Saccharomyces cerevisiae to lead ion stress

The response of Saccharomyces cerevisiae to different concentrations of Pb(2+) was investigated. The results demonstrated that the growth of S. cerevisiae in the presence of Pb(2+) showed a lag phase much longer than that in the absence of Pb(2+). The inhibition was dependent upon Pb(2+) concentrations. The Pb(2+) at a concentration of 5 microM inhibited the microbial growth by approximately 30% with regard to control, whereas Pb(2+) at concentration of 2 microM did not have a significant effect on the microbial growth. The existence of Pb(2+) did not perturb cell-protein synthesis and there was a good correlation between dry cell weights and total protein content (R (2) = 0.98). The RNA/DNA ratio in the microbial cells varied with Pb(2+) concentration and there was a significant positive correlation between Pb(2+) concentration and the RNA/DNA ratio. The microbial assimilation of ammonium ion was inhibited by the presence of Pb(2+) in the medium; when Pb(2+) concentration was 10 microM, the microbial ammonium assimilation was inhibited about 50%, in comparison with the control experiment.