Whole genome-based phylogenetic analysis of Rickettsiae

Rickettsiae are obligate intracellular bacteria associated with arthropods, often pathogenic for humans. The Rickettsia genus belongs to the Alphaproteobacteria; it was divided into three major subgroups, mainly on the basis of phenotypic and serological features: the typhus group (TG), made of Rickettsia prowazekii and R. typhi, the spotted fever group (SFG) including R. conorii, R. africae, R. massiliae, R. akari, R. felis and several other validated species, and a group of marginal and divergent species including R. bellii and R. canadensis. Rickettsia spp. express few remarkable phenotypic characteristics. Therefore, their precise identification and phylogenetic classification have mainly relied on the analysis of molecular sequences. Phylogenetic analysis based on 16S rDNA gene sequences has frequently been