Assessing variability of endosymbiotic ciliates (Litostomatea, Trichostomatia) using 18S rDNA and ITS region

Endosymbiotic ciliates of the subclass Trichostomatia (Litostomatea) live in the digestive tract of various vertebrates. Trichostomes show remarkable morphological diversity, which has yet to be studied thoroughly using molecular methods. In this paper, we investigated intraspecific variability of three species (Cochliatoxum periachtum, Tripalmaria dogieli, and Cycloposthium edentatum) from the intestine of equids for the first time. Two molecular markers were used, the 18S rDNA and the internal transcribed spacer (ITS) region, the latter of which is often considered a robust molecular marker for the recognition of closely related taxonomic groups. We analyzed 182 sequences of the 18S rRNA gene and 141 sequences of the ITS region from both rumen and intestinal ciliates, belonging to different families within the orders Vestibuliferida, Entodiniomorphida, and Macropodiniida. Both original and publicly available data were used. The differences in variability of both molecular markers for representatives of different genera and families of ciliates were compared.