%0 Journal Article
%T Antifreeze Water-Rich Dormant Cysts of the Terrestrial Ciliate Colpoda cucullus Nag-1 at −65 ℃: Possible Involvement of Ultra-Antifreeze Polysaccharides
%A Matsuoka, Tatsuomi
%A Sogame, Yoichiro
%A Nakamura, Rikiya
%A Hasegawa, Yuya
%A Arikawa, Mikihiko
%A Suizu, Futoshi
%J Acta Protozoologica
%V 2020
%R 10.4467/16890027AP.20.011.13266
%N Volume 59, Issue 3-4
%P 141-147
%K water-rich resting cyst, antifreeze, polysaccharides, osmolarity
%@ 0065-1583
%D 2021
%U 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
%X 
	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.