Action spectra in ultraviolet wavelengths (150-250 nm) for inactivation and mutagenesis of Bacillus subtilis spores obtained with synchrotron radiation

Bacillus subtilis spores were exposed in vacuo to monochromatic UV radiation from synchrotron radiation in the wavelength range of 150-250 nm. Survival and frequency of mutation to histidine-independent reversion were analysed for three types of spores differing in DNA-repair capabilities. UVR spores (wild-type DNA repair capability) exhibited nearly equal sensitivity to the lethal effects of far-UV (220nm and 250nm) and of vacuum-UV radiation (150 and 165nm), but showed marked resistance to 190nm radiation. UVS spores (excision-repair and spore-repair deficient) and UVP spores (a DNA polymerase I-defective derivative of UVS) exhibited similar action spectra; pronounced sensitivity at 250 and 220 nm, insensitivity at 190 nm and a gradual increase of the sensitivity as the wavelength decreased to 165 nm. In all strains, the action spectra for mutation induction paralleled those for the inactivation, indicating that the vacuum-UV radiation induced lethal and mutagenic damages in the spore DNA. The insensitivity of the spores to wavelengths around 190 nm may be explicable by assuming that radiation is absorbed by materials surrounding the core in which DNA is situated. (author)