A novel phenomenon of pseudoencystment in free living ciliate Pseudourostyla levis (Ciliophora, Hypotrichia) from River Yamuna, Delhi

Abstract

Free living ciliates are exposed to environmental challenges such as starvation, temperature fluctuations, high population density and salinity variations. Ciliates lower their metabolic activity and form cysts, an adaptive strategy evolved in response to environmental stress. In the present study on Pseudourostyla levis, a novel phenomenon of pseudoencystment had been noticed in which cells entered a state of dormancy but did not secrete a cyst wall. The process of pseudoencystment, which physiologically resembled true encystment, was functionally unrelated to it and was thus designated as pseudoencystment. Unlike true cysts, pseudocysts remained dormant for about 12 hours and then reverted to the active trophic state without any change in the environmental conditions. Another unique feature of pseudoencystment, was the synchronized induction of pseudocysts formation, achieved by a brief spell of starvation and the pseudocysts reverted to active trophic state without any change in environmental conditions. The state of dormancy did not provide any long-term protection to the ciliate and appeared to be a short term adaptation to the environment. The present study aimed to analyze the parameters for the induction of pseudocyst formation, cortical topological changes and to study the possible significance of this process. However, occasionally true cysts were also obtained by prolonged starvation, lasting 3-4 days but true cysts required either food or a fresh culture medium for excystation.