ACTION PROPERTIES OF HYI KILLER TOXIN FROM WILLIOPSIS-SATURNUS VAR. SATURNUS, AND ANTIBIOTICS, ACULEACIN-A AND PAPULACANDIN-B

The mechanism of the killing and cytocidal effects produced by HYI tox in from Williopsis saturnus var. saturnus, and by the amphiphilic anti biotics aculeacin A and papulacandin B on yeast Saccharomyces bayanus cells was studied. When the yeast cells were treated with these molecu les, a discharge of cell materials at the budding position was observe d by phase-contrast and scanning electron microscopy, The cytocidal ef fect of these molecules was most pronounced when the cells were in the logarithmic growth phase. Washing the HYI toxin incubation mixture co mpletely eliminated the killing activity, but in the case of the antib iotics, it only partially reduced the cytocidal activity. Full recover y of the killing activity in the supernatant of the washing solution w as observed after HYI toxin incubation, but in the case of the antibio tics, the recovery of cytocidal activity was time-dependent. The activ ity of membrane beta-1,3-glucan synthase was potently inhibited by HYI toxin, and the concentration of this enzyme in the budding tip was ob served. These results suggest that HYI toxin exerts a cytocidal effect on the budding of sensitive yeast cells by inhibiting fell wall synth esis. This mechanism is similar to that of the HM-1 toxin of W. saturn us var. mrakii, and to aculeacin A and papulacandin B, although there are some differences from that of HYI toxin.