The complete mitochondrial genome of Orientobilharzia turkestanicum supports its affinity with African Schistosoma spp.

Orientobilharzia turkestanicum is a blood fluke of many mammals and causes orientobilharziasis that is also a neglected parasitic zoonosis because the cercaria of O. turkestanicum can infect humans and cause cercarial dermatitis. The present study determined the complete sequence of mt genome of O. turkestanicum and revised its phylogenetic position based on mt gene content and arrangement. The complete mtDNA sequence of O. turkestanicum was 14,755 bp in length, which is slightly larger than the mtDNA genomes of three species of the blood flukes, Schistosoma mekongi (14,072 bp), Schistosoma japonicum (14,085 bp) and Schistosoma mansoni (14,415 bp), but smaller than Schistosoma haematobium (15,003 bp) and Schistosoma spindale (16,901 bp). The mt genome of O. turkestanicum contains 12 protein-coding genes, 22 transfer RNA genes and two ribosomal RNA genes, but lacks an atp8 gene, consistent with that of Schistosoma species. The mt genome arrangement of O. turkestanicum contains an AT-rich region and two non-coding regions (NCRs), including long non-coding region (LNR) and short non-coding region (SNR). Phylogenetic analysis based on amino acids sequences showed that O. turkestanicum belonged to the genus Schistosoma, and is phylogenetically closer to the African schistosome group (S. haematobium, S. spindale and S. mansoni) than to the Asian group (S. mekongi and S. japonicum). But the arrangement of mtDNA protein-coding genes for O. turkestanicum is the same as Asian group, and distinct from the African species. Combining content and arrangement of mtDNA for O. turkestanicum, we conclude that O. turkestanicum should be considered a member of the Schistosoma genus, which shares a closer affinity to the African schistosomes than the Asian species, and gene order of mt genome in O. turkestanicum would be considered sympleisiomorphic (perhaps retained from the ancestor).