Resting cysts: A survival strategy in Protozoa Ciliophora

Encystment is a reversible cell differentiation process that also requires an antagonistic process, i.e. excystment. Both processes are genetically encoded. Encystment is of common occurrence among free-living ciliates and may serve several different purposes. In some ciliates, this process is part of the regular life cycle (reproductive cyst), while many other ciliates undergo encystment when environmental conditions become adverse (resting cyst). In this review, the different phases and aspects of the encystment process in ciliates, such as the ecological role, the cyst formation, the morphological characteristics of the cysts and their dynamic state during the time and the excysting process are reviewed on the basis on our own results and literature data.