The variations of sensitivity to gamma irradiation during the progression of E. coli B and E. coli${\rm B}_{{\rm S}-2}$ through various phases of growth were compared with the ability of the same cells to break down their DNA during postirradiation incubation. DNA degradation was measured under the conditions that minimize the reincorporation of breakdown products. Both the survival and the DNA degradation varied during the cell progression in a very similar manner: the lowest radiosensitivity and the lowest DNA degradation were found in the stationary phase, while the cells from midlogarithmic phase displayed the lowest survival and the most extensive degradation. Among several strains examined, the strains of higher radio-resistance showed lower ability to break down their DNA; moreover, radio-sensitive phases of their growth displayed also higher degradation of DNA. A general correlation showing a direct proportionality of the percentage of degradation and the negative logarithm of survival was obtained. It is proposed that the degradation of DNA in E. coli is not a part of the repair process.

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Copyright 1969 Academic Press, Inc.
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