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 F₁₀ values, were as follows: AB1157 (wild type), 3.9; AB1886 ( uvrA rec⁺ ), 3.3; AB2463 ( uvr⁺ recA ), 4.6; and AB2480 (uvrA recA), 1.04. A large oxygen enhancement also was observed for the 365-nm induced increase in 254-nm lethality in strains AB1157 and AB1886. H...