8-METHOXYPSORALEN EFFECTS ON SURVIVAL AND REPAIR OF ESCHERICHIA-COLI AFTER ULTRAVIOLET-IRRADIATION - ACTION SPECTRA

The action spectra of two strains of Escherichia coli over the wavelength range of 254 to 390 nm has been obtained in the presence of 8-methoxypsoralen (8-MOP). Strains WP2 (wild-type) and WP2Hcr (uvrA) showed greatly enhanced (102- to 103-fold) photosensitivity from 390 to 310 nm, the greatest effect appearing at 320 to 335 nm. At wavelengths from 300 to 254 nm the presence of 8-MOP produced no effect on lethal sensitization with WP2Hcr cells, but the WP2 strain exhibited a two-fold protection when 8-MOP was present. 8-MOP has a major absorption peak at 304 nm, the region of the least biological effect. The large shoulders on the survival curves of untreated cells of both strains irradiated at wavelengths above 300 nm was significantly diminished by the presence of 8-MOP. If such shoulders are caused by fluence-dependent repair processes, using the reciprocal of the 'shoulder fluence', F(q), as a measure of the rate of production of sublethal damage, it appears that 8-MOP-sensitized damage is not repaired as efficiently as damage induced in the absence of 8-MOP. Two small regions in the action spectra were exceptions to this generality: The region of 300-315 nm for the WP2Hcr strain and of 300-285 nm for the WP2 strain.