Synergism between 365- and 254-nm Radiations for Inactivation of Escherichia coli

The lethal interaction between radiations at 254 and 365 nm was studied in strains of Escherichia coli K12 that differ in repair capability. Increased sensitivity to 254-nm radiation was produced by a prior exposure to large fluences of 365-nm radiation for both stationary-phase and exponential-phase cells of strains K12 AB1157 (wild type) and K12 AB1886 (excision deficient). Results presented support the hypothesis that damage by 365-nm radiation to recombination and excision repair is a major cause of synergism between 365- and 254-nm radiations and a major factor in 365-nm inactivation of strains proficient in postreplication and/or excision repair. The interaction between 365- and 254-nm radiations in the postreplication repair-deficient strain (K12 AB2463) was complex: The 254-nm sensitivity decreased at relatively low fluences of 365-nm radiation (< 8 x 10/sup 5/ J m/sup -2/), but increased relative to the minimum value at greater fluences. The decrease in 254-nm sensitivity after a low fluence at 365 nm reflects the phenomenon of photoprotection, while the increase in 254-nm sensitivity at high 365-nm fluences supports the previous reports of 365-nm damage to the excision-repair system. The strong lethal synergism of 365- and 254-nm radiations was much greater in the radiation-resistant organism Micrococcus radiodurans thanmore » in E. coli.« less