Further insights into the phylogeny of facultative parasitic ciliates associated with tetrahymenosis (Ciliophora, Oligohymenophorea) based on multigene data

Tetrahymenosis, caused by about 10 Tetrahymena species, is an emerging problem inflicting a significant economic loss on the aquaculture industry worldwide. However, in the order Tetrahymenida, there are many unresolved evolutionary relationships among taxa. Here we report 21 new sequences, including SSU-rRNA, ITS1-5.8S-ITS2 rRNA and LSU-rRNA, genes of 10 facultative parasitic Tetrahymena associated with tetrahymenosis, and conduct phylogenetic analyses based on each individual gene and a three-gene concatenated dataset. The main findings are: (1) All the parasitic and facultative parasitic species cluster in borealis group. (2) With the addition of new sequences, Tetrahymena is still divided into three groups, namely the borealis group, the australis group, and the paravorax group. (3) the cluster pattern of all the newly sequenced facultative parasitic Tetrahymena species shows that members of the borealis group may be more susceptible to parasitism. (4) phylogeny based on concatenated genes show that T. pyriformis, T. setosa, and T. leucophrys have close relationship.

Automated summary

Tetrahymenosis, caused by 10 Tetrahymena species, is a rising problem in the aquaculture industry, and the evolutionary relationships among Tetrahymena taxa remain unresolved. This study reports 21 new sequences from 10 facultative parasitic Tetrahymena associated with tetrahymenosis, and conducts phylogenetic analyses based on individual genes and a three-gene concatenated dataset. The main findings are: (1) Parasitic and facultative parasitic species cluster in the borealis group. (2) Tetrahymena is divided into borealis, australis, and paravorax groups. (3) Borealis group members may be more susceptible to parasitism. (4) T. pyriformis, T. setosa, and T. leucophrys have a close relationship based on concatenated genes.