Susceptibility of individual cells of Saccharomyces cerevisiae to the killer toxin K1

The susceptibility of sensitive yeast to killer toxins is known to depend o n various factors, such as the selected killer toxin, the exposed yeast str ain, its growth phase and the state of culture under given experimental con ditions. The aim of this paper was to find whether individual cells from on e culture are equally susceptible to the impact of the killer toxin, For th is purpose the rhodamine B assay in a modified form was used. In order to o bserve the fate of individual cell the method of fluorescence video microsc opy with a digital picture analysis was applied, Four selected groups of sp ecific cells (with no, small, medium, and large bud, respectively) were inv estigated. Different sensitivity of Saccharomyces cerevisiae cells to the k iller toxin KI was observed in these cell groups. The most susceptible appe ared 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 sus ceptibility in S-phase results probably from coincidence in higher porosity of the cell wall, accumulation of surface receptors, and enlarged growth a ctivity at the surface cell structures. (C) 2001 Academic Press.