Electron microscope and genetic analysis of an intracellular bacterium associated with the common rough woodlouse, Porcellio scaber (Isopoda, Porcellionidae)

The common rough woodlouse, Porcellio scaber, is a common and widespread isopod species of Western and Northern Europe. A previously unknown intracellular bacterium has been identified in a diseased Porcellio larva. Microscopic studies revealed the subcellular structures characteristic of infection by Rickettsiella-like bacteria. Molecular phylogenetic analysis based on the 16S ribosomal RNA encoding rrs gene demonstrated that the woodlouse pathogen belongs to the taxonomic genus Rickettsiella (Gammaproteobacteria; Legionellales). Moreover, genetic analysis makes it likely that this new pathotype should be considered a member of the “Rickettsiella armadillidii complex”, i.e. a group of Rickettsiella bacteria found mainly in terrestrial isopods. R. armadillidii is currently placed in synonymy with the nomenclatural type species, Rickettsiella popilliae. The present study does not lend support to this synonymization.