INDUCED RESISTANCE TO GAMMA IRRADIATION IN ESCHERICHIA COLI

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Abstract
Survivors of an initial gamma-ray irradiation were used as inoculum for the next culture to be irradiated and so on. E. coli, strain 15, showed an increasing susceptibility to radiation injury. Using the same technics it was possible to induce radio-resistance in both strains B and B/r of this organism. The reproduction frequency over the 3-hr. irradiation period was found to be 0.15 and the initial mutation ration (mutants produced per roentgen) was estimated at 4 x 10-7 for strain B and 5 x 10-6 for B/r. A method for estimating the number of resistant cells present in a culture under radiation is developed and illustrated from the survival curve data.