Encystment/excystment response and serotypic variation  in the gastropod parasite Tetrahymena rostrata  (Ciliophora, Tetrahymenidae).
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.
P
P
Segade
N
N
García
J M
JM
García Estévez
C
C
Arias
R
R
Iglesias
D000383:Agriculture; D000818:Animals; D006372:Helix, Snails / Q000469:parasitology*; D007106:Immune Sera / Q000276:immunology; D007668:Kidney / Q000469:parasitology; D051379:Mice; D008810:Mice, Inbred C57BL; D046529:Microscopy, Electron, Transmission; D008900:Mineral Waters / Q000469:parasitology; D012987:Soil / Q000737:chemistry / Q000469:parasitology; D013030:Spain; D013696:Temperature; D013768:Tetrahymena / Q000502:physiology* / Q000648:ultrastructure
D007106:Immune Sera; D008900:Mineral Waters; D012987:Soil