Inactivation of microorganisms by vacuum ultraviolet radiation

Abstract

We describe the effects of vacuum ultraviolet light (λ=173nm) on the microfungus species Cladosporium herbarum, Rhodotorula colostri, and Saccharomyces cerevisiae. The survival probability was found to depend on the fungus concentration in the sample, which indicates that a shadowing effect may be responsible. The survival probabilities of the microfungi during the exponential growth phase were independent of fungus species, and this may result from insufficient accumulation of protective pigment in the cell wall. Infrared spectroscopy and atomic force microscopy of irradiated samples show breakdown of sugars and proteins in the cell wall. Electrophoresis revealed double-strand breaks in the DNA of Rhodotorula colostri but not Cladosporium herbarum, which may be because the latter produces the protective pigment melanin. When antioxidants (GSH, I₂, KI) were added to the culture medium, the microfungi showed improved survival probability, indicating that an indirect mechanism is contributing to the inactivation process. The contribution of this indirect mechanism reached 50% for energy densities of 5−20mJ/cm².