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Cooperative association between insects that exploit restricted nutrients and symbiotic bacteria are common in nature. Endosymbionts, in many insects, are transmitted vertically and provide nutrients for their host, but this beneficial long term relationship puts constrains on both host and symboint adaptive interactions. To protect long-term endosymbionts from the immune response of host’s system, symbionts are placed in bacteria bearing host cells called bacteriome. Genomic and evolutionary data have shown that major deletions and mutations of genes occur in endosymbionts, some of which are involved in bacterial virulence and host tolerance. In order to investigate the immune specificities of bacteriocytes, there were studies with the Sitophilus genus which share a intracellular symbiosis with a Gram-negative y-Proteobacterium called Sitophilus primary endosymbiont (SPE). SPE induces a systematic respond that leads to the up-regulation of one antimicrobial peptide-encoding gene coleoptericin-A (col A). Through the use of RNA interference, PCR, and fluorescence in situ hybridization (FISH), researchers were able to identify col A in the symbiosis. Col A plays two important roles to immunity and symbiosis. It acts as the first line of defense against microbial intrusion and regulation of endosymbiont number and location. This supports the idea that long-term coevolution may have selected Col A for this symbiotic function.

                                       Figure shows FISH visualization of SPE 9 days (upper panels) and 14 days (lower panels).


Login F.H., Balmand S., Vallier A., et al. (2011). Antimicrobial peptides keep insects endosymbionts under control. Science, 334. 362-365. doi: 10.1126/science.1209728