Effects of polymyxin B sulfate and polymyxin B nonapeptide on growth and permeability of the yeast Saccharomyces cerevisiae.

Polymyxin B, a toxic, membrane-affecting antibiotic, can be rendered harmless to yeast cells by enzymatic removal of its fatty acyl moiety. The remaining cyclic peptide portion, polymyxin B nonapeptide, has no significant effect on growth and viability but it drastically reduces mating efficiency. In addition, the cyclic peptide enhances sensitivity of cells to several drugs, presumably by increasing membrane permeability. Mutants resistant to polymyxin B are simultaneously less responsive to the combination of the nonapeptide and the drugs. This indicates that the peptide portion of polymyxin B is the moiety responsible for the permeability changes. The resistance is inherited as a simple recessive trait. The mutation has been mapped to chromosome XV of Saccharomyces cerevisiae.