Mitochondrial genome sequencing and analysis of scuticociliates (<i>Uronema marinum</i>) isolated from <i>Takifugu rubripes</i>

Abstract

Scuticociliates are dangerous parasitic pathogens for in worldwide mariculture. Scuticociliates cause high mortality to marine fish. After an outbreak of scuticociliatosis in <i>Takifugu rubripes</i> in Liaoning Province, northern China, <i>Uronema marinum</i>, a scuticociliate, was identified. In this study, using Illumina MiSeq next-generation sequencing, the mitochondrial genome of <i>U. marinum</i> was assembled and analysed phylogenetically using mitochondrial genomes of other scuticociliates. The complete <i>U. marinum</i> mitochondrial genome was 39,845 bp; it contained two rRNAs, six tRNAs, and 39 protein-coding genes (PCGs). From the 39 PCGs, 15 PCGs were located on the heavy strand, and 24 PCGs on the light strand of <i>U. marinum</i> mitogenome. The phylogenetic tree showed that there were two main clades, Oligohymenophorea and Spirotrichea. Nine ciliate species were clustered together within Oligohymenophorea; <i>Uronema marinum</i> was a separate cluster sharing a relatively close ancestry with Hymenostomatida. The results of this study will help advance the systematics, and studies of evolution and molecular epidemiology of scuticociliates.