Influence of preirradiational and postirradiational heating of lyophilized Micrococcus radioproteolyticus cells on their survival

The survival curve of Micrococcus radioproteolyticus following gamma irradiation of lyophilized cells is characterized by a broad shoulder reaching as far as the dose range 10 - 20 kGy (1 - 2 Mrad). The course of the curve indicates that under these conditions most of the changes induced by irradiation have the character of sublethal damage, which the cell can repair. The course of the survival curve does not change if the lyophilized cells are heated prior to irradiation for 2 h at 60 0C. Certain changes do occur if the preirradiational temperature is 80 0C. If the cells are exposed to increased temperature after irradiation even a temperature of 60 0C brings about a marked decrease in survival. A temperature of 80 0C after irradiation leads to extensive changes in the shape of survival curves, which are characterized by a narrowing or even disappearing of the shoulders. It can be concluded from the results obtained that an increased temperature modifies the capability of irradiated lyophilized cells to repair radiation damage. (author)