Saccharomyces cerevisiae is used in this study not only as a test organism for routine quick toxicity screening but also as a potential indicator of DNA damage by chemicals. Several indices were investigated for evaluating the inhibition rates caused by some heavy metals. Specific growth rate proved to be the most suitable index. Of the chemicals used in this study CH3HgCl was the most toxic with an EC60of 3.5×10−4 mmol/l. The EC60's for HgCl2. CdCl2 and NiCl2 were 0.192, 0.0345 and 2.30 mmol/l respectively, using specific growth rate as an index. The interacting effect between Cd and Ni was generally additive. In order to detect DNA damage the growth of wild type strains was compared with the growth of strains deficient in one or all the DNA repairing systems. A known mutagen, 4-nitroquinoneline 1-oxide, and a non-mutagen, kanamycin, were used. The experimental results confirmed that 4-nitroquinoneline 1-oxide damaged the DNA of Saccharomyces cerevisiae, while kanamycin did not damage it. The importance of this confirmation lies in the fact that this test uses Saccharomyces cerevisiae, which is a eucaryotic organism and closer to human being than the procaryotic organisms that are usually used in other mutagenicity tests such as Ames test and Rec-assay.

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