Director Max Planck Institute for Chemical Ecology Jena, Thuringen, Germany
Symbiotic associations with microbes are important driving forces of evolutionary innovation. Several insects engage in symbiotic alliances that protect their immature stages against pathogen infection through the production of antimicrobial compounds. However, little is known about the dynamics of defensive alliances and the molecular factors underlying the establishment of symbiosis. Darkling beetles of the genus Lagria engage in a defensive symbiosis with multiple Burkholderia strains as well as other bacteria that protect the developing egg from fungal pathogens. Using manipulative bioassays and mass spectrometry imaging, we discovered that symbiont-mediated protection extends throughout the larval stages, facilitated by morphological adaptations allowing for the release of the symbionts and symbiont-produced secondary metabolites to the surface during molting. Furthermore, using a culturable and genetically tractable Burkholderia symbiont strain, we investigate the molecular factors that are important for host colonization by transposon insertion sequencing after passaging a random transposon mutant library through beetle larvae. The results reveal motility, stress response genes, as well as certain secondary metabolite genes as important for successful symbiosis establishment. The Lagria symbiosis presents an experimentally and genetically tractable system to study the ecological relevance and evolutionary dynamics of defensive symbioses as well as the molecular underpinnings of the host-symbiont interaction.
