Indirect action of VUV radiation on micro-organisms

Abstract

The contribution of the indirect mechanism to the inactivation of microorganisms by long wavelength VUV radiation (λ>170 nm) was investigated in this work. For these purposes dry spores of microscopic fungi Rhodotorula colostri and Saccharomyces cerevisiae were irradiated by Xe excilamp (λ= 173 nm).To determine the contribution of indirect action to the microfungi inactivation, the survival probabilities of the samples grown on a nutrient medium containing antioxidant (I₂) and without it were carried out. The results have shown, that the survival probabilities of the spores containing antioxidant increases by no less than 20-25% compared to control ones. The increase value depends on VUV irradiation dose and microorganism type. It should be emphasized, that due to the masking of microfungi survival by I₂ bactericidal action, the obtained survival probability increase values should be considered as a lower estimate. Electrophoresis of microfungi DNA have shown, that VUV irradiation of spores containing antioxidants leads to less DNA destruction and heaver DNA fragments appearance. The latter may indicate a decrease of reactive oxygen species effect on DNA in the presence of antioxidants. Atomic force microscopy and IR spectroscopy haven’t shown influence of antioxidant on cell wall destruction. This can indicate, that in contrast to wet spores, in the case of VUV irradiation of dry ones, the indirect mechanism of cell wall destruction is absent or weakly expressed.