ACTION SPECTRA FOR OXYGEN‐DEPENDENT AND INDEPENDENT INACTIVATION OF ESCHERZCHZA COLZ WP2s FROM 254 TO 460 NM*

Abstract

Abstract— Action spectra for lethality of E. coli WP2s under aerobic and anaerobic conditions. based on final slopes of the survival curves, reveal the absence of oxygen dependence at 313 nm and shorter wavelengths and a strong oxygen dependence (OER of 12 at 334 nm and 16 at 365 nm) at wavelengths longer than 313 nm. Shoulders or small peaks at340, 365, 410 and 500 nm suggest the participation of non‐DNA chromophores in aerobic lethality at these wavelength ranges.

Lethality by 365nm Radiation inEscherichia ColiK12 AB2480 in the Presence and Absence of Maximal Photoreactivation Under Aerobic and Anaerobic Conditions

“…Oxygen dependence was not significant at 365 nm with strain AB2480 in the absence of photoreactivation . This result supports previous reports of the absence of oxygen dependence for lethality at 365 nm with this strain (Tyrrell 1976, Webb andBrown 1979b) . However, there was a strong oxygen enhancement of 365 nm lethality when the irradiated cells were subjected to maximal PR (figure 1) .…”

“…Furthermore, the production of cyclobutyl pyrimidine dimers by gamma radiation was demonstrated by chemical assay (Wang and Smith 1978) . A strong oxygen enhancement has been obtained for lethal effects with both 365 nm (Tyrrell 1976, Webb andBrown 1979 a, b) and gamma radiation (Vinicombe et al . 1978) in repair-proficient, uvrA rec + , uvr + recA and polA strains .…”

“…Stringent anoxia was obtained by a method previously reported in detail (Webb and Brown 1979 a) . Cell suspensions were maintained at 0°C (liquid) or 25°C during irradiation at 365 nm and 25°C during irradiation at 254 rim .…”

“…The absence of oxygen dependence for the inactivation of the double repairdeficient strain, Escherichia coli K12 AB2480 (uvrA recA) at the near-ultraviolet (near-UV) wavelength 365 nm, contrasts strikingly with the large oxygen dependence of single repair-deficient and repair-proficient strains for inactivation at the same wavelength (Tyrrell 1976, Webb andBrown 1979 a, b) . The basis of the strong oxygen enhancement for lethality obtained for near-UV radiation (320-400 nm) has not been established , Webb 1977, Webb and Brown 1979 .…”

“…The basis of the strong oxygen enhancement for lethality obtained for near-UV radiation (320-400 nm) has not been established , Webb 1977, Webb and Brown 1979 . Although cyclobutyl pyrimidine dimers (Tyrrell 1973) and DNA single-strand breaks (Tyrrell, Ley andWebb 1974, Ley, Sedita andBoye 1978) are produced in biologically significant yields, the role of these and other DNA lesions has not been determined for oxygen-dependent lethality in wild-type and single repair-deficient strains (Tyrrell 1976, Webb, Brown and .…”