Analysis of the ITS region and partial ssu and lsu rRNA genes ofBlastocystisandProteromonas lacertae

Abstract

Blastocystisis a common single-celled enteric parasite found in a large variety of hosts. Recent molecular analysis supports the concept that this eukaryotic organism is a stramenopile most closely related toProteromonas lacertae, a parasite of reptiles. In this study, the internal transcribed spacer region, partial small subunit rRNA and large subunit rRNA genes from 7Blastocystisisolates (5 human, 1 pig and 1 sheep), and aProteromonas lacertaeisolate were amplified by PCR, cloned and sequenced.Blastocystiswas found to be a typical eukaryote with both ITS1 and ITS2 regions present. Phylogenetic analysis based on the entire PCR amplicon revealed that theBlastocystisisolates did not segregate according to host or geographic origin. The highest sequence identities with the conservedBlastocystis5·8S rDNA sequence were with the stramenopilesFibrocapsa japonica,Chattonella marina,Cylindrotheca closteriumandHyphochytrium catenoides. The most parsimonious tree based on the 5·8S rDNA sequence fromP. lacertae, 11 other stramenopiles, 2 fungi, 3 algae and 3 alveolates showedBlastocystispositioned within the stramenopiles, withP. lacertaeas its closest relative. This work therefore supports the hypothesis thatBlastocystisis most closely related toP. lacertae, and that it should be regarded as an unusual stramenopile.