Comparative sensitivity of escherichia coli between gamma-rays and ultraviolet-rays

It is well known that the action to living organisms by ionizing radiation or ultraviolet is induced by DNA damage in the cell. The surviving fraction of cells and shapes of a survival curve are to determine the relative sensitivity of microorganisms. In this study, three strains of E. coli B/r, B and B1 were used for comparative sensitivities of gamma and ultraviolet irradiation plating on either Trypton agar of Glucose-NH4 agar plates. From this study, high erresistance on survival fraction was observed on the strain B/r at gamma irradiation compared with strains of B and B1. In case of ultraviolet irradiation, resistance of B/r was not remarkable compared with other strains. From the result of comparative sensitivities on the plating media, effect of photoreactivation was clearly observed on the strain B after ultraviolet irradiation. Strain B1 is a mutant on reduced photoreactivation which showed similar pattern of survival fraction on the different plating media as like to gamma irradiation. Strain B/r should be to have strong ability of dark repair systems compared with photoreactivation systems after ultraviolet irradiation. Higher repair of cell damage on strain B/r at gamma irradiation is indicating that the enzymatic repair of damaged DNA by gamma-rays is easily available compared with ultraviolet irradiation. (author)