Pseudomonas – insect interactions
Recently, we discovered that a subgroup of root-colonizing pseudomonads, represented by Pseudomonas protegens and Pseudomonas chlororaphis, exhibits not only antifungal, but also potent oral and systemic insecticidal activity, in particular towards larvae of different lepidopteran pests. Following ingestion by the insect larvae, the bacteria colonize the gut, thereby possibly competing with the resident microbiota. They then cross the intestinal epithelial barrier by an as yet unknown mechanism and invade the hemocoel where they proliferate and cause deadly sepsis.
A large insecticidal protein that we termed the Fit toxin makes an important contribution to insect pathogenicity. Remarkably, the Fit toxin is related to the Mcf toxins of the entomopathogenic nematode symbionts Photorhabdus and Xenorhabdus. Fit insect toxin expression in the pseudomonads is activated in a host-specific manner during infection of the insect host, but not during colonization of plant roots. Detection of the host environment and activation of insect toxin production is mastered by a sensor histidine kinase-response regulator hybrid protein which during its evolution recruited, via a domain shuffling event, a common sensor domain from a regulatory protein involved in control of nutrient uptake.
It is likely that other, yet to be discovered, factors relevant for insect interaction are also expressed in a host-dependent manner. We are currently inspecting several exoproducts and cell envelope-associated components for their contribution to fitness, competitiveness and immune evasion of the entomopathogenic pseudomonads.