Mutants of Saccharomyces cerevisiae resistant to a quaternary ammonium salt

Three quaternary ammonium salts were compared in respect of their ability to select resistant mutants of S. cerevisiae. The mutants tolerating slightly higher IM compound concentration were analysed. They appeared to be the products of nuclear gene mutation segregating monogenically but strongly influenced by genetic background. The mutant IMR when transformed to rho degrees lost resistance below the level of minimal inhibitory concentration of original strain. Possible hypothesis explaining this phenomenon is presented.