ABSTRACT
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 254 nm (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 >315 nm 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 photo-induced 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.
