Changes in Radiosensitivity of Streptomyces cacaoi Spores during Germination

Changes in sensitivity to gamma and ultraviolet radiations of germinating spores of Streptomyces cacaoi var. asoensis were investigated. The results obtained are as follows: (1) The period highly sensitive to gamma irradiation was found at about 100 to 110 min of incubation in a germination medium, which was different in the timing from that sensitive to heat. (2) The patterns of changes in sensitivity to gamma and ultraviolet radiations during germination were not identical. (3) The presence of chloramphenicol in the germination medium remarkably abolished changes in radiosensitivity of spores during the germination treatment. Mitomycin C also inhibited the development of radiation resistance during the late phase of germination. (4) Radioprotective effects of freezing and ethanol as a radical scavenger lead us to the view that indirect-type actions of radiation on spores may operate in increase of radiosensitivity during the early phase of germination. (5) The scheme for phase transitions in sensitivities to gamma and ultraviolet radiations during germination was presented in relation to the macromolecular synthesis and heat resistance. Different patterns of the time course were observed on sensitivities to gamma and ultraviolet radiations and heat.