DNA analysis of a radiotolerant bacterium Pantoea agglomerans by FT-IR spectroscopy

A radiation tolerance strain, Pantoea agglomerans was isolated from γ-irradiated carrot samples (Daucus carota). D₁₀ determination showed that the radioresistance of this bacterium is five-fold higher than Escherichia coli, both belonging to the family of Enterobacteriaceae. DNA isolated from untreated and irradiated bacterial cells was analyzed by FT-IR spectroscopy to investigate the radiotolerance of this bacterium. At doses <5 kGy, an alteration of the interbase hydrogen networks was observed and characterized mainly by an increase of bands assigned to the carbonyl non-pairing and the free amine groups. Moderate breakage of the DNA backbone and damage of the osidic structure were also observed. Similar spectral profiles were noticed at doses ≥5 kGy, but additional increase of the band intensity of CC and CN suggests damages of nucleobases. High number of asymmetric PO₂⁻ and upper shift of symmetric PO₂⁻ are indicative of DNA strand breaks. Osidic damages were evidenced by decrease of the absorption bands ascribed to deoxyribosyl moieties and by appearance of C–OH band. DNA degradation at high irradiation doses was also noticed by electrophoresis using agarose gel. It appeared that DNA underwent covalent cross-linking, as revealed by agglomeration of DNA in the wells of agarose gel.