Genomic Comparison of Insect Gut Symbionts from Divergent Subclades.

Stink bugs of the superfamilies Coreoidea and Lygaeoidea establish gut symbioses with environmentally acquired bacteria of the genus sensu lato. In the genus , the stink bug-associated strains form a monophyletic clade, named stink bug-associated beneficial and environmental (SBE) clade (or ). Recently, we revealed that members of the family Largidae of the superfamily Pyrrhocoroidea are associated with but not specifically with the SBE ; largid bugs harbor symbionts that belong to a clade of plant-associated group of , called plant-associated beneficial and environmental (PBE) clade (or ). To understand the genomic features of symbionts of stink bugs, we isolated two symbiotic strains from a bordered plant bug (Pyrrhocoroidea: Largidae) and determined their complete genomes. The genome sizes of the insect-associated PBE (iPBE) are 9.5 Mb and 11.2 Mb, both of which are larger than the genomes of the SBE symbionts. A whole-genome comparison between two iPBE symbionts and three SBE symbionts highlighted that all previously reported symbiosis factors are shared and that 282 genes are specifically conserved in the five stink bug symbionts, over one-third of which have unknown function. Among the symbiont-specific genes, about 40 genes formed a cluster in all five symbionts; this suggests a "symbiotic island" in the genome of stink bug-associated .