Discovery of Novel Rickettsiella spp. in Ixodid Ticks from Western Canada

Abstract

ABSTRACTThe genomic DNA from four species of ixodid ticks in western Canada was tested for the presence ofRickettsiellaby PCR analyses targeting the 16S rRNA gene. Eighty-eight percent of theIxodes angustus(n= 270), 43% of theI. sculptus(n= 61), and 4% of theI. kingi(n= 93) individuals examined were PCR positive forRickettsiella, whereas there was no evidence for the presence ofRickettsiellainDermacentor andersoni(n= 45). Three different single-strand conformation polymorphism profiles of the 16S rRNA gene were detected among amplicons derived fromRickettsiella-positive ticks, each corresponding to a different sequence type. Furthermore, each sequence type was associated with a different tick species. Phylogenetic analyses of sequence data of the 16S rRNA gene and three other genes (rpsA,gidA, andsucB) revealed that all three sequence types were placed in a clade that contained species and pathotypes of the genusRickettsiella. The bacterium inI. kingirepresented the sister taxon to theRickettsiellainI. sculptus, and both formed a clade withRickettsiellagryllifrom crickets (Gryllus bimaculatus) and “R. ixodidis” fromI. woodi. In contrast, theRickettsiellainI. angustuswas not a member of this clade but was placed external to the clade comprising the pathotypes ofR. popilliae. The results indicate the existence of at least two new species ofRickettsiella: one inI. angustusand another inI. kingiandI. sculptus. However, theRickettsiellastrains inI. kingiandI. sculptusmay also represent different species because each had unique sequences for all four genes.