The Relationship between Growth and Survival after Irradiation of Escherichia coli Strain B and two Resistant Mutants

Abstract

Faster growth of Escherichia coli strain B cells was observed on media which contain factors which accelerate the lethal effect of radiation. Incubation in the presence of metabolic inhibitors after irradiation stimulates irradiated cells to originate colonies. Holding the cells on complete media at low temperatures after irradiation causes increased death of irradiated cells, an exception to the principle that the greater survival of strain B is associated with slower growth. The difference in the radiosensitivity of strain B and 2 resistant mutants, strains B/r and Bpr5, depends on differences in their utilization of organic nutrients, since: (i) all 3 strains have about the same sensitivity if they are plated on a minimal medium; (ii) if strains B and B/r are treated with chloramphenicol immediately after UV, the survival of strain B increases, and that of strain B/r decreases, both reaching the same level as if they had been plated immediately on minimal medium; (iii) if irradiated cells of strains B and B/r are incubated on nutrient medium for a short period before chloramphenicol treatment, the survival of strain B roughly equals that of the resistant mutants, while that of B/r is unaffected. When logarithmic phase broth-grown cells of all 3 strains are exposed to visible light after UV, only strain B is "photoreactivated", and then only when viable counts on nutrient medium are compared, the counts on synthetic medium being unaffected by the visible light.