Mickey S. Brown

SENSITIVITY OF STRAINS OF ESCHERICHIA COLI DIFFERING IN REPAIR CAPABILITY TO FAR UV, NEAR UV AND VISIBLE RADIATIONS†

Abstract— In stationary phase, strains of Escherichia coli deficient in excision (B/r Her) or recombination repair (K.12 AB2463) were more sensitive than a repair proficient strain (B/r) to monochromatic near‐ultraviolet (365 nm) and visible (460 nm) radiations. The relative increase in sensitivity of mutants deficient in excision or recombination repair, in comparision to the wildtype, was less at 365 nm than at 254 nm. However, a strain deficient in both excision and recombination repair (K12 AB2480) showed a large, almost equal, increase in sensitivity over mutants deficient in either excision or recombination repair at 365 nm and 254 nm. All strains tested were highly resistant to 650 nm radiation. Action spectra for lethality of strains B/r and B/r Her in stationary phase reveal small peaks or shoulders in the 330–340, 400–410 and 490–510 nm wavelength ranges. The presence of 5μg/ml acriflavine (an inhibitor of repair) in the plating medium greatly increased the sensitivity of strain B/r to radiation at 254, 365 and 460 nm, while strains E. coli B/r Her and K12 AB2463 were sensitized by small amounts. At each of the wavelengths tested, acriflavine in the plating medium had at most a small effect on E. coli K.12 AB2480. Acriflavine failed to sensitize any strain tested at 650 nm. Evidence supports the interpretation that lesions induced in DNA by 365 nm and 460 nm radiations play the major role in the inactivation of E. coli by these wavelengths. Single‐strand breaks (or alkali‐labile bonds), but not pyrimidine dimers are candidates for the lethal DNA lesions in uvrA and repair proficient strains. At high fluences lethality may be enhanced by damage to the excision and recombination repair systems.

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

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.

DESTRUCTION OF PHOTOREACTIVATING ENZYME BY 365 nm RADIATION

Abstract— Following the observation that in vivo photoreactivation of 365‐nm‐induced pyrimidine dimers could not be observed chemically, a study was made of the inactivation of photoreactivating enzyme activity by this near‐ultraviolet wavelength. It was observed that: (1) Dimers induced in extracted bacterial DNA by 365 nm radiation are completely photoreactivable and are monomerized as an exponential function of the photoreactivation time. (2) Photoreactivability of 254‐nm‐induced damage in Escherichia coli B/r Hcr is progressively destroyed in vivo as a function of the dose of 365 nm radiation. (3) The ability of the yeast photoreactivating enzyme to monomerize dimers induced at 365 nm in bacterial DNA is destroyed in vitro as a function of the dose of 365 nm radiation, and at a rate comparable to killing of E. coli. These results are consistent with biological measurements which indicate that photoreactivability of ultraviolet (near and far) lethal damage is reduced by exposure of the bacteria to 365 nm radiation.

[Action spectra for lethality in recombination-less strains of Salmonella typhimurium and Escherichia coli].

Abstract— Action spectra for lethality of both stationary and exponentially growing cells of recombinationless (recA) mutants of Salmonella typhimurium and Escherichia coli were obtained. Maximum sensitivity was observed at 260nm which corresponds to the maximum absorbance of DNA. However, a shoulder occurred in the 280–300 nm range that departed significantly from the absorption spectrum of DNA. At wavelengths longer than 320nm, the shapes of inactivation curves departed significantly from those at wavelengths shorter than 320nm and survival curves at wavelengths longer than 320nm had a large shoulder. A small peak or shoulder occurred in the 330–340nm region of the action spectra. The special sensitivity of recA mutants to broad spectrum near‐UV radiation may be due to synergistic effects of different wavelengths. Parallels between the inactivation of recA mutants and the induction of a photoproduct of l‐tryptophan toxic for recA mutants (now known to be H2O2) suggest that H2O2 photoproduct from endogenous tryptophan may be involved in the high sensitivity of these strains to broad spectrum near‐UV radiation.

Lethal effects of pyrimidine dimers induced at 365 nm in strains of E. coli differing in repair capability.

Photoreactivation (PR) after 365-nm inactivation was measured in four strains of Escherichia coli differing in repair capability. Photoreactivation was observed in the recA strains K12 AB2480 and K12 AB2463 indicating a significant role of pyrimidine dimers in the lethal action of 365-nm radiation in these strains. Significant PR was not observed in the uvrA strain, K12 AB1886, or in the repair proficient strain, K12 AB1157, after 365-nm inactivation. Biological evidence indicated that stationary phase cells had not lost the capacity for photo-enzymatic repair after fluences of 365-nm radiation of 2 X 10(6) J/m-2 or less. It is proposed that pyrimidine dimers, although induced, are not significant 365-nm lethal lesions in uvrA and wild-type strains because of their efficient dark repair.

Oxygen Dependence of Sensitization to 254-nm Radiation by Prior Exposure to 365-nm Radiation in Strains of Escherichia coli K12 Differing in DNA Repair Capability

Near-ultraviolet radiation (320-400 nm) can produce both lethal and mutagenic effects in bacteria and other biological systems. It has been proposed that biological effects associated with DNA lesions produced by far-uv, near-uv, and X radiation are enhanced by near-uv damage to the DNA repair systems. The relationships between oxygen dependence of enhancement of sensitivity to 254-nm radiation by prior irradiation at 365 nm and the oxygen dependence of inactivation by 365-nm radiation were investigated in strains of Escherichia coli K12 differing in DNA repair capability. The oxygen enhancement ratios (OER) of the four E. coli K12 strains tested, based on 365-nm

NONRECIPROCAL SYNERGISTIC LETHAL INTERACTION BETWEEN 365‐nm and 405‐nm RADIATION IN WILD TYPE and uvrA STRAINS OF ESCHERICHIA COLI*

{\rm F}_{10}

Photoreactivation of 365 nm inactivation in Escherichia coli

values, were as follows: AB1157 (wild type), 3.9; AB1886 (

Synergism between 365- and 254-nm radiations for inactivation of Escherichia coli

uvrA\ rec^{+}

Lethality by 365nm Radiation in Escherichia Coli K12 AB2480 in the Presence and Absence of Maximal Photoreactivation Under Aerobic and Anaerobic Conditions

), 3.3; AB2463 (