Resting cyst formation is a crucial process of cryptobiosis in protists. In colpodid ciliates, cyst formation is accompanied by large-scale morphological changes such as changes of cell shape, resorption of cilia, and formation of a cyst wall; additionally, the cell cycle is arrested. These changes provide acquired tolerance against environmental stresses. During cyst formation, mitochondrial membrane potential is reduced and the level of the ATP synthase beta chain is suppressed, strongly indicating that metabolism has ceased. Here, however, we show that ATP levels are elevated during the initial phases of encystment implying that metabolism may not be completely suppressed. This finding suggests another aspect of resting cyst formation that is not applicable to cryptobiosis.
