Predominance of membrane damage in yeast cells in suspension with monochromatic 163-nm vacuum ultraviolet light

Effects of monochromatic 163-nm ultraviolet light on aqueous suspensions of yeast cells were studied under N2 and O2 bubbling conditions. This is a continuation of previous attempts at using a bromine resonance lamp immersed in cell suspension as a means of treating cells with water radicals (163-nm photons decompose water molecules into H atoms and OH' radicals). We found that inactivation occurred only under O2 bubbling. Genetic changes were induced, but this was attributed to the effects of far-uv components which contaminate the emission. A characteristic feature of the vacuum uv inactivation was a decrease in survival when cells were held in liquid after irradiation. The presence of p-nitrosodimethylaniline (a known OH' scavenger) during irradiation prevented the O2-dependent enhancement of inactivation. Cells irradiated under N2 bubbling showed no such enhancement. Thus, the fast access of oxygen is a necessary condition for fixing initial damage. Initial damage of this type seems to be amplified during subsequent incubation, causing further killing. Cells irradiated under N2 bubbling were not, however, free of damage, since dye permeability across the cell membrane of irradiated samples increased markedly with both N2 and O2 as tested by photodynamic induction of genetic changes using normally unpenetrable dye as a sensitizer. Spectrophotometric evidence for the presence of toluidine blue in the irradiated cells are also presented