Effect of the products generated by the vacuum ultraviolet photolysis of water on the survival of microorganisms

Subject of study. The indirect mechanism of the effect of vacuum ultraviolet (VUV) radiation on the survival of microorganisms was studied. Aim of study. The aim was to compare the effectiveness of reactive products generated by the VUV photolysis (Δ λ =166−182nm) of water that act from outside and inside the biological cell on the survival of microorganisms. In addition, changes in the VUV radiation spectrum passing through micrometer-thick layers of water and concentrations of photolysis products formed during this process were determined. Method . In this study, microscopic fungi Rhodotorula colostri (dry and covered with a water layer) were irradiated with VUV radiation from xenon excimer lamps. The spectral composition of the radiation and the changes in it when passing through water layers were determined both experimentally and computationally. The concentrations of the water photolysis products were calculated by numerical simulations. The survival of the microorganisms was assessed by colony counting, and the influence of reactive products from intracellular water photolysis was evaluated by adding antioxidants to the nutrient medium. Main results. Upon irradiation through a water layer, the survival probabilities increased by an average of 60% for spores without antioxidants and by 40% for spores with antioxidants compared with those for dry spores. This increase is attributed to reduced photochemical activity due to the absorption of the short-wavelength radiation ( λ <170nm) and less effective action of reactive photolysis products from outside the cell compared with those from inside the cell. The short-wavelength region ( λ <170nm) of the xenon excimer emission band was almost completely absorbed when the radiation passed through a water layer with a thickness of d >1µm. The main reactive products of the VUV photolysis of water were identified as H 2 O 2 , HO 2 ⋅ , and ⋅OH, with concentrations of the order of 10 14 cm −3 . Practical significance. The results can be applied in disinfection technologies using short-wavelength ultraviolet radiation and in addressing challenges in space biology.