Genomic analyses of Rickettsiella endosymbionts revealed putative distinctive phenotypic effects in arthropods

Members of the Rickettsiella genus (order: Legionellales) are emerging as widespread intracellular bacteria associated with insects, arachnids, and crustaceans, some of them being?entomopathogens and some being?maternally inherited endosymbionts.?However, the genomic diversity of Rickettsiella remains largely unexplored, and their genetic potential to induce complex phenotypes in arthropods is only partially understood.?In this study, we sequenced and assembled five novel genomes of Rickettsiella strains isolated from three tick species and applied?comparative genomics. We observed that Rickettsiella members share similar metabolic capabilities, including pathways involved in energy production, but collectively lack virulence genes from pathogenic Legionellales.?Additional analysis of Rickettsiella genomes reveals significant variability in genomic and metabolic properties related to endosymbiosis (B vitamins biosynthesis, heme metabolism, cif genes). Phylogenomics further revealed that tick-borne Rickettsiella do not cluster within a tick-specific subclade. Instead, they exhibit distinct evolutionary origins within the genus, indicating that Rickettsiella have undergone repeated horizontal transfers between ticks and other arthropods, such as aphids and woodlice.