Gamma Radiation Tolerance and Protein Carbonylation Caused by Irradiation of Resting Cysts in the Free-living Ciliated Protist Colpoda cucullus

Abstract

The ciliate Colpoda cucullus forms resting cysts to survive unfavorable environmental stresses. In this study, we have shown that Colpoda resting cysts survived exposure to a gamma radiation dose of 4000 Gy, although vegetative cells were killed by 500 Gy. After 4000 Gy irradiation, more than 90% of resting cysts and approximately 70% of dry cysts could excyst to form vegetative cells. In both cases, the excystment gradually increased after the induction of excystment. In addition, we also showed that protein carbonylation level was increased by gamma irradiation, but decreased by incubation in the cyst state. These results indicated that cell damage was repaired in resting cysts. Colpoda probably developed tolerance to gamma radiation by forming resting cysts as a strategy for growth in terrestrial environments, as part of contending with the stress due to reactive oxygen species caused by desiccation.

Can Colpoda travel across oceans? Salinity tolerance of resting cysts may enable global dispersal of the species.

“…The expression of genes related to stress responses and oxidoreductase activity showed upregulation, while other metabolic processes displayed down-regulation. Our results of this study support our previous claim that resting cysts are not just resting but repairing cell damages even though they cease mitochondrial metabolic activity (56), i.e., carbonylated proteins induced by gamma irradiation have been shown to be repaired in resting cysts (37). Differential gene expression during the early stage of encystment has been shown previously in transcriptomic studies of Colpoda aspera (57) and Pseudourostyla cristata (58); these observations demonstrated the presence of an early signaling pathway for encystment as had been suggested earlier (59,60).…”

“…The vegetative cells were induced by En-medium with or without 0.3% NaCl. The encystment rate was calculated as described previously (37).…”

“…The pellet was solubilized in SDS-sample buffer and boiled for 3 min. SDS-PAGE and western blotting on PVDF membranes were performed as described previously (37). Enzymatic digestion of proteins on PVDF membranes was as previously described (46).…”

New Strategy for Effective Biosynthesis of Chiral Aryl Alcohols: Co-Cultivation Microbe with Natural Deep-Eutectic Solvent

“…It might be the reason that Geotrichum candidium cells could maintain better metabolic activity through this new strategy. It was reported that the damage of ciliate Colpoda cucullus by gamma irradiation was decreased when incubated in the cyst . Therefore, it was reasonable to speculate that G.…”

“…It was reported that the damage of ciliate Colpoda cucullus by gamma irradiation was decreased when incubated in the cyst. 31 Therefore, it was reasonable to speculate that G. candidium cells could be capable of repairing the cell damage suffered from ChCl/Lys (1:2) addition in growth duration.…”