Host group adaptation of “Candidatus Rickettsiella isopodorum”, a lineage of intracellular gamma-proteobacterial pathogens carried by woodlice

The taxonomic genus Rickettsiella (Gammaproteobacteria; Legionellales) comprises intracellular bacteria associated with a wide range of arthropods including insects, arachnids and crustaceans that are currently under intensive evaluation as possible sources of new biocontrol agents. A multilocus sequence analysis approach has been employed to independently evaluate the previously established 16S rRNA based phylogeny for two Rickettsiella strains associated with isopods from California and Germany. Phylogenetic reconstruction from three protein-encoding marker genes, namely ftsY, gidA, and sucB, confirms the very tight phylogenetic relationship of Rickettsiella bacteria from closely related hosts, but distant geographic origins. These findings are consistent with stable host group – pathogen relationships within the Rickettsiella.