The susceptibility of sensitive yeast to killer toxins is known to depend on various factors, such as the selected killer toxin, the exposed yeast strain, its growth phase and the state of culture under given experimental conditions. The aim of this paper was to find whether individual cells from one culture are equally susceptible to the impact of the killer toxin, For this purpose the rhodamine B assay in a modified form was used. In order to observe the fate of individual cell the method of fluorescence video microscopy with a digital picture analysis was applied, Four selected groups of specific cells (with no, small, medium, and large bud, respectively) were investigated. Different sensitivity of Saccharomyces cerevisiae cells to the killer toxin KI was observed in these cell groups. The most susceptible appeared to be the cells which were in S-phase (cells with the small buds); the least susceptible were the M-phase cells with large buds. The enhanced susceptibility in S-phase results probably from coincidence in higher porosity of the cell wall, accumulation of surface receptors, and enlarged growth activity at the surface cell structures. (C) 2001 Academic Press.
