The mitochondrial genome of the ciliate Pseudourostyla cristata (Ciliophora, Urostylida)

Abstract

The mitochondrial genomes (mitogenomes) of ciliates are linear and relatively large (<80 kb). Until now, only 11 ciliate mitogenomes, either partial or complete, have been reported. The aim of the present study was to characterize the mitogenome of Pseudourostyla cristata (Ciliophora, Urostylida). The resulting mitogenome represents the first complete mitogenome for order Urostylida and is the largest sequenced ciliate mitogenome (~76 kb), containing 31 protein-coding genes, nine transfer RNAs (tRNAs), two ribosomal RNAs (rRNAs), and 21 unclassified open reading frames. Among the 11 ciliates whose mitogenomes have been identified, the mitogenome of P. cristata is most similar to that of Oxytricha trifallax, which is in the same subclass. However, the mitogenome of P. cristata is missing two genes (nad3 and nad6) and three split genes (nad4, nad5, and rpl6) that are found in the mitogenome of O. trifallax. Furthermore, the locations of the protein-coding and tRNA genes in P. cristata are different than those of the same genes in either Euplotes minuta or E. crassus, even though the species belong to the same class. This suggests that mitogenome structure is unlikely conserved in class level phylogenetic comparison.