VARIATIONS IN THE SENSITIVITY OF ESCHERICHIA COLI TO IONIZING RADIATIONS DURING THE GROWTH CYCLE

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Abstract
The X- and gamma ray sensitivity of Escherichia coli B/r was studied as a function of the age of the culture. Cells, from a stationary phase culture, inoculated into fresh nutrient broth show the usual phases of the cultural cycle and changes in radiation sensitivity characteristics of the various phases. Cells from the lag phase are more radioresistant than cells from elsewhere in the cycle, and yield sigmoidal rather than the usual exponential survival curves, suggesting a multi-nucleate or multicellular nature. Cells from the logarithmic phase are exceedingly sensitive except at reduced post-irradiation incubation temperatures, suggesting that the abnormal sensitivity may be related to the relative inability of these rapidly dividing cells to recover from the damaging effects of irradiation. At the end of the logarithmic phase cells return to the same sensitivity as displayed by cells in the maximum stationary phase in routine culturing. Some of the findings concerning variations in sensitivity to radiation can be correlated with findings of other investigators on the sensitivity to other physical and chemical agents.