Effects induced by XeCl laser radiation and germicidal lamp radiation on E. coli strains survival and mutability

In this work the mutagenic effect on Escherichia coli strains induced by UV radiation emitted by a XeCl laser (λ = 308 nm) has been analysed as a function of the exposure dose and compared with the effect induced by 254 nm radiation emitted by a conventional germicidal lamp. E. coli strains, wild-type (recA+) and mutant (recA1, defective in DNA damage repair systems), plated on LB agar, supplemented with rifampicin when requested, were irradiated by means of a germicidal lamp in the dose range 0 - 9 mJ/cm2. Similar strains were exposed to 308 nm pulsed laser radiation (τ = 20 ns FWHM; max. pulse energy: 100 mJ) in the dose range 0-1.0 x 104 mJ/cm2. The discrepancy between the results obtained with the lamp and the laser on the mutation frequency, suggested that the biological response to the two radiation sources involves distinct mechanisms. This hypothesis was supported by the evidence that exposure to near-UV 308 nm induced mutagenesis in the recA-defective strain at an extent considerably higher than in the recA-proficient strain.