Osmotic-Sensitive Mutants of Saccharomyces cerevisiae as Screening Organisms for Promutagens and Procarcinogens

Abstract

An attempt to improve the response of yeast cells to promutagens and procarcinogens in mutagenicity assay was made by using osmotic-sensitive mutants of a yeast, Saccharomyces cerevisiae. Four osmotic-sensitive mutants of yeast which showed increased sensitivity to 1.5 M KCl were induced by ethylmethanesulfonate treatment. One of the mutants, strain C658-K42, was highly sensitive to antibiotics such as mitomycin C, novobiocin, nalidixic acid, chloroquine and rifampicin at concentrations showing no growth-inhibitory effect on the original strain, S. cerevisiae C658. Strain C658-K42 was considered to have a defect in the cell membrane. These osmotic-sensitive mutants were tested for suitability for screening by using well-known procarcinogens (promutagens), dimethylnitrosamine, 3, 4-benzpyrene and 2-acetylaminofluorene. The response of these mutants in a mutagenicity assay (Trp⁺ reversion) was apparently increased compared with that of the original strain. The yeast cells which were harvested from a late logarithmic phase culture could activate procarcinogens to genetically active forms without any exogeneously added metabolic activation system.