The taxonomic position of the entomopathogenic bacterium Rickettsiella grylli: 16S rRNA genes and beyond

The genus Rickettsiella of insect pathogenic bacteria has previously been assigned to the γ- proteobacterial order Legionellales, family Coxiellaceae, on the basis of the determination of a 16S rRNA encoding sequence from a strain of the species Rickettsiella grylli. Subsequently, conflicting results have been reported with other Rickettsiella pathotypes. Here we have used the 16S rRNA gene from a second R. grylli strain as well as the deduced sequences for two proteins, the chaperonin GroEL and the ortholog of a Coxiella burnetii factor triggering capsule synthesis, MucZ, to check for a corroboration of this taxonomic classification. While our study lends strong support to the classification at the order level, the assignment to the family Coxiellaceae appears much less obvious from our results.