Candidate pathogenicity islands in the genome of ' Rickettsiella isopodorum', an intracellular bacterium infecting terrestrial isopod crustaceans.

The bacterial genus belongs to the order Legionellales in the Gammaproteobacteria, and consists of several described species and pathotypes, most of which are considered to be intracellular pathogens infecting arthropods. Two members of this genus, and , are known to infect terrestrial isopod crustaceans. In this study, we assembled a draft genomic sequence for , and performed a comparative genomic analysis with . We found evidence for several candidate genomic island regions in , none of which appear in the previously available genome sequenceFurthermore, one of these genomic island candidates in contained a gene that encodes a cytotoxin partially homologous to those found in and (Enterobacteriaceae), suggesting that horizontal gene transfer may have played a role in the evolution of pathogenicity in . These results lay the groundwork for future studies on the mechanisms underlying pathogenesis in , and this system may provide a good model for studying the evolution of host-microbe interactions in nature.