TY - JOUR
TI - Antifreeze Water-Rich Dormant Cysts of the Terrestrial Ciliate Colpoda cucullus Nag-1 at −65 ℃: Possible Involvement of Ultra-Antifreeze Polysaccharides
AU - Matsuoka, Tatsuomi
AU - Sogame, Yoichiro
AU - Nakamura, Rikiya
AU - Hasegawa, Yuya
AU - Arikawa, Mikihiko
AU - Suizu, Futoshi
TI - Antifreeze Water-Rich Dormant Cysts of the Terrestrial Ciliate Colpoda cucullus Nag-1 at −65 ℃: Possible Involvement of Ultra-Antifreeze Polysaccharides
AB - 
	We found that the water-rich (osmolality below 0.052 Osm/l) wet resting cysts of the soil ciliate Colpoda cucullus Nag-1 were tolerant to extremely low temperature (−65℃). When cell fluid obtained from the resting cysts was cooled at −65℃, small particles of ice crystals did not grow into large ice crystals. At −65℃, the cysts shrank due to an outflow of water, because a vapor pressure difference was produced between the cell interior and freezing surrounding medium. The osmolality of these shrunk cells was estimated 0.55 Osm/l, and the freezing point depression of the shrunk cell fluid was estimated to be 1.02℃. Hence, the antifreeze ability of wet cysts at −65℃can not be explained by freezing point depression due to elevation of cytoplasmic osmolality.

	The cytoplasm of resting cysts was vividly stained red with periodic acid-Schiff (PAS) and stained purple with toluidine blue. On the other hand, the excystment-induced cysts were not stained with PAS, and exhibited a loss of the antifreeze activity. PAS staining of SDSPAGE gel obtained from encysting Colpoda cells showed that a large amount of PAS-positive macromolecules accumulated as the encystment stage progressed. These results suggest that antifreeze polysaccharides may be involved in the antifreeze activity of C. cucullus Nag-1 dormant forms.
VL - 2020
IS - Volume 59, Issue 3-4
PY - 2021
SN - 0065-1583
C1 - 1689-0027
SP - 141
EP - 147
DO - 10.4467/16890027AP.20.011.13266
UR - https://ejournals.eu/en/journal/acta-protozoologica/article/antifreeze-water-rich-dormant-cysts-of-the-terrestrial-ciliate-colpoda-cucullus-nag-1-at-65-possible-involvement-of-ultra-antifreeze-polysaccharides
KW - water-rich resting cyst
KW - antifreeze
KW - polysaccharides
KW - osmolarity