Evidence of Stress Recovery in Free-Living Ciliate Colpoda cucullus: The Repair Capability of Resting Cysts to Damage Caused by Gamma Irradiation

In this study, we report that the unicellular free-living protist Colpoda cucullus in the resting cyst (cryptobiosis) repairs stress damage. We previously demonstrated that resting cysts of Colpoda cucullus have extreme tolerance to gamma irradiation and can revert to vegetative cells after irradiation. Such irradiated cysts gradually excyst, suggesting that stress repair mechanisms are active during excystment or in the resting cyst. Herein we provide bioassay evidence that the rate of excystment of irradiated cysts is elevated by subsequent incubation, thereby indicating that cells injured by gamma irradiation can repair themselves in the resting cyst, whereas irradiated dry cysts cannot.