The effect of pH and temperature on the lysis of yeast cells by cationic dyes and surfactants

Conductivity measurements in yeast suspensions, to which a stepwise increasing quantity of a cytolytic reagent was added, provided evidence towards explaining possible mechanisms of cytolysis by cationic dyes and by cationic surfactants. These lytic cations are bound to the cell surface. If uptake exceeds a critical amount, the permeability barrier of part of the yeast cells in the suspension is destroyed. The “threshold” amount of lytic agent was proportional to the quantity of yeast in the suspension, and was pH‐ and temperature dependent in a way which suggested an interaction with anionic membrane lipids. There were similarities between the cationic dyes, Toluidine Blue and Azure A, and the cationic surfactants, cetrimide and cetylpyridinium chloride, in their cytolytic effect on yeast cells. A mechanism of membrane breakdown is discussed.