Sensitivity to polychromatic UV-radiation of strains of Deinococcus radiodurans differing in their DNA repair capacity

Purpose: To characterize the ultraviolet (UV) sensitivity and establish the UV-induced DNA damage profile of cells of four Deinococcus radiodurans strains. The investigated strains differ in their radiation susceptibility, leading to a classification into a UV-sensitive (UVS78 and 1R1A) and a UV-resistant class (wild type strain R1 and 262). Materials and methods: Deinococcus radiodurans cells were exposed in suspension to monochromatic 254nm (UV-C) and polychromatic UV radiations; the surviving fraction was determined by assessing the ability of the bacteria to form colonies. The UV-induced DNA lesions were measured quantitatively using an accurate and highly specific assay that involves the combination of high performance liquid chromatography (HPLC) with tandem mass spectrometry detection. Results: Analysis of the DNA photoproducts showed that the TC (6-4) photoproduct and the TT and TC cyclobutane dimers were the major lesions induced by UV-C and UV-(>200 nm)-radiation. The UV- sensitive class was approx. 10 times more susceptible to UV- C and UV-(>200 nm)- radiations than the resistant class. Interestingly, the survival curves of all investigated strains become similar with longer UV wavelengths in the UV-(>315 nm)- radiation range. This observation suggests that the repair mechanisms of the UV- resistant class are not specifically effective for damage produced by UV of the >315nm range. However, the initial amount of DNA photoproducts produced upon irradiation was found to be the same in resistant and sensitive strains for each wavelength range. Conclusion: Compared to mammalian cells, the DNA of Deinococcus radiodurans cells is less susceptible to the photoinduced formation of thymine cyclobutane dimers as inferred from comparative analysis. The ongoing investigations may contribute to a better understanding of the mechanism of DNA photoprotection against the direct effects of UV radiation. This may be of interest in the present context of a possible continuous decrease in the ozone layer thickness.