Molecular phylogeny of Blastocystis isolates from wild rodents captured in Indonesia and Japan

Blastocystis sp. is a common intestinal protist found worldwide in a variety of animals, including humans. Currently, 17 subtypes (STs) of Blastocystis isolates from mammalian and avian host species have been reported based on the small subunit ribosomal RNA gene (SSU rDNA). Among these, human Blastocystis were only identified among STs 1-9. Except ST9, all other STs comprised isolates from humans and other animal species. Entire sequence data of the SSU rDNA of nine Blastocystis isolates from laboratory rats or guinea pigs previously showed ST4, whereas Blastocystis isolates from wild rodents have not been addressed genetically. In this study, Blastocystis infection in wild rodents was surveyed in Indonesia and Japan, and 11 and 12 rodent Blastocystis parasites were obtained from Rattus exulans and R. novercious, respectively. All new Blastocystis isolates from wild rodents were identified as ST4 based on the SSU rDNA sequences. The best tree inferred with the entire sequences of the SSU rDNA of all ST4 isolates including 17 data registered in GenBank clearly showed monophyletic ST4A and ST4B clades. Although ST4 isolates from laboratory rats were separated into these two clades, all Blastocystis isolates from wild rodents in the present study were positioned into the clade ST4A and further separated into two sub-clusters within the clade ST4A according to the location of the host species. Considering the fact that laboratory rats were susceptible to both ST4A and ST4B, separation of the monophyletic sub-clusters of Blastocystis isolates from Indonesian Polynesian rats and Japanese brown rats may indicate the presence of geographical variations rather than a host-specific separation. In either way, the robust host preference to rodent species of ST4 Blastocystis was also confirmed.