Lack of induction of non-targeted mutations in intact bacteriophage by UVB (313 nm), UVA (334 nm, 365 nm) and visible (405 nm) irradiation of host cells

Mutation to virulence has been measured in intact bacteriophage lambda 15 infected into host cells pre-treated with UVC (254 nm), UVB (313 nm), UVA (334 nm, 365 nm) or visible (405 nm) radiations. We have confirmed that UVC radiation leads to a large enhancement (maximum enhancement factor of 140 in wild-type) of the background spontaneous mutation frequency (non-targeted mutagenesis) and have further shown that this is at least partially dependent on excision repair (maximum enhancement factor of 14 in uvrA strain). In contrast, UVB (313 nm) radiation enhances the mutation frequency by less than a factor of 2. Longer wavelength UVA radiation (334 nm, 365 nm) actually reduces the mutation frequency to 25% of the background levels presumably by reducing the levels of viral replication occurring in the host cells. A visible wavelength (405 nm) has no effect on mutation frequency over the fluence range employed.