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Encystment/excystment response and serotypic variation in the gastropod parasite Tetrahymena rostrata (Ciliophora, Tetrahymenidae)

Author:
Segade, P., García, N., García Estévez, J. M., Arias, C., Iglesias, R.
Source:
Parasitology research 2016 v.115 no.2 pp. 771-777
ISSN:
0932-0113
Subject:
Helix aspersa, Tetrahymena, autogamy, encystment, excystation, farming systems, farms, kidneys, mineral water, mucus, parasites, serotypes, snails, soil, starvation, temperature, Spain
Abstract:
Tetrahymena rostrata, which is characterized by a particular encystment-excystment cycle involving autogamy, has been recently found infecting the kidney of edible Helix aspersa snails under farming conditions. In this work, the effects of several factors on its encystment/excystment behaviour and the occurrence of different serotypes were investigated. The encystment/excystment response under starvation conditions was seriously affected by temperature. While a peak of encystment at 48 h followed by a progressive spontaneous excystment was observed at 18 and 25 °C, the encystment response was practically inhibited at 5 °C and clearly slowed down at 10 °C. At 30 °C, most of surviving ciliates remained encysted throughout the experiment, with spontaneous excystment being detected only after switching the temperature to 18 °C. Soil components also affected the encystment/excystment behaviour at 18 °C, with spontaneous excystment occurring in the presence of a sterile-filtered soil extract or mineral water but being strongly minimized with a non-filtered soil extract. Resting cysts formed in the latter extract exhibited a 3–4 times thicker and ultrastructurally more complex wall than that formed in mineral water and retained the excystment ability for about 4 weeks. Incomplete desiccation did not affect significantly the encystment response, while the mucus and kidney extracts from snails as well as a ciliate extract strongly stimulated a rapid excystment. Finally, two different serotypes infecting H. aspersa in heliciculture farms of Galicia (NW Spain) were identified, but no differences were observed between the encystment/excystment responses exhibited by two isolates belonging to each serotype.
Agid:
4796522