Interactions between uv radiation of different energies in the inactivation of bacteria

A strong lethal interaction was observed between various monochromatic wavelengths (254, 334, 365, and 405 nm) in the repair-proficient E. coli K-12 strain AB 1157, except in the case of preexposure to 405-nm radiation which resulted in a protection against the inactivation resulting from subsequent exposure to 365-or 254-nm radiations. The results may be tentatively explained by assuming two classes of DNA lesions and two classes of damage to repair (reversible and inrreversible) whose proportions vary according to wavelength.