The Relationship of Radioresistance to Balanced Growth-rate in Micrococcus Radiodurans

Summary

The changes in the macromolecular composition of Micrococcus radiodurans with increasing medium-determined growth-rate are similar to such alterations in more radiosensitive bacterial strains. As the growth-rate and quantity of cellular macromolecules increase, the x-radiation sensitivity tends to increase when measured by the D₀ or the LD₉₀ exposure. The amounts of endogenous, possibly radioprotective sulphydryls do not account for the increased radiosensitivity. It is also found that the assay of cells on minimal agar generally improves the survival after irradiation. These findings in M. radiodurans suggest that damage to DNA and to the division mechanisms of the cells may account for the heightened radiosensitivity found in conditions of rapid growth.