Characterization of the Complete Mitochondrial Genome of Pleurogenoides japonicus (Digenea, Pleurogenidae): Comparison With the Members of Microphalloidea and Phylogenetic Implications

Pleurogenoides japonicus (Trematoda: Microphalloidea) is an important parasite in wood frogs with high infection rates and significant ecological, economic, and societal importance. The scarcity of molecular data for these parasites severely limits population genetics and phylogenetic studies. In the present study, for the first time, we determined and described the entire mitochondrial (mt) genome of P. japonicus as the first representative of the family Pleurogenidae. The entire mt genome of P. japonicus was circular, with 15,043 bp (GenBank accession number OR900118), containing 36 genes, comprising 12 protein-coding genes (cox1-3, nad1-6, nad4L, cytb, and atp6), two ribosomal RNA genes, 22 transfer RNA genes, and two non-coding regions. There were 23 intergenic spacers, ranging from 2 to 162 bp, and only one 40 bp overlap between nad4L and nad4 genes in the P. japonicus mt genome. The nucleotide composition of P. japonicus mt genome exhibited a strong AT bias with a 63.75% A + T content, while the AT- and GC-skews were - 0.435 and 0.407, respectively. Comparative analysis demonstrated that the P. japonicus mt genome shared the most common characteristics with Microphalloidea trematodes, and the cox1 gene was the longest and most conserved gene in Microphalloidea trematodes. The gene arrangements of Xiphidiata trematodes were of the same order based on protein-coding genes and rRNA genes, except for tRNA. More than two gene arrangement types exist in Echinostomata and Xiphidiata, and the gene rearrangement events mainly occurred in "trnE-trnG" and "trnG-trnE". Phylogenetic analysis suggested that trematodes of the family Pleurogenidae clustered more with Prosthogonimidae than Eucotylidae. The mt genome data of P. japonicus provide an accurate genetic marker for further studies of Xiphidiata trematodes.