Photoreactivation in Vitamin B1-requiring Escherichia coli

Abstract

It has been known that ultraviolet (UV) irradiation causes mutation and death in many organisms, and that UV-inactivated organisms can be photoreactivated.The present paper describes the photoreactivation in vitamin B1-requiring mutants of E. coli B. Three kinds of mutants, which require respectively pyrimidine, thiazole and VB1, were isolated. The cells of wild strain and three mutants were irradiated with UV light of 255mμ at the rate of 0.194mW/cm2. After irradiation the cells were immediately exposed to photo reactivating (PR) light of 320-420mμ for 15 to 60 minutes.The survival curves of Th-, B1- mutants were similar to that of the wild strain, but Pm- mutant was extremely sensitive to UV irradiation.When cells were irradiated by UV light at a dose of 40×0.194mW/cm2, the wild strain was almost completely reactivated by exposure to PR light for 15 minutes, and Th-, B1- mutants were reactivated in 60 minutes. However, in Pm- mutant, the phenomenon of photoreactivation was not observed.After irradiation of UV light at a dose of 80×0.194mW/cm2, only the wild strain was reactivated by exposure to PR light for 60 minutes. On the other hand, none of three mutants could be reactivated.The present results indicated that in the wild strain and VB1-requiring mutants of E. coli B, UV-induced damage was repaired by exposure to PR light, although the photoreactivating ability of mutants was lower than that of the wild strain. It was concluded that the photoreactivating activity differs by the kind of mutants and the degree of UV damage.