Excretory/secretory products of entomopathogenic nematodes and their role in the host-parasite interaction
Školitel: doc. RNDr. Pavel Hyršl, Ph.D.
Instituce: Masaryk University, Faculty of Science
Obor: Animal Physiology
O mém projektu
Entomopathogenic nematodes (EPNs) are the obligate parasites of insects. Only larval stages so called infective juveniles are free-living in the soil. They seek for a suitable host to complete their development cycle. Significant representatives of entomopathogenic nematodes are genus Heterorhabditis and Steinernema. EPNs live in symbiotic relationship with entomopathogenic bacteria (Heterorhabditis - Photorhabdus, Steinernema – Xenorhabdus) that are pathogenic to insect similarly to nematodes themselves and both organisms together creates nematobacterial complex highly effective against many insect species. Entomopathogenic nematodes are related with human parasites. This also one of the reasons why they are studied. In the fight against the immune system of insect, nematodes use their excreted/secreted products (ESPs), which infective juveniles have partly in their bodies and partly induced in further development after EPNs infect their host. These products are a mixture of molecules with distinct functions. The entomopathogenic nematodes are partly able to produces the excreted/secreted product by themselves and partly in the cooperation with symbiotic bacteria5. A number of molecules were already described by Sterinernema carpocapsae. Parasitic stages of a virulent strains contain higher amounts of proteolytic activity than a low virulent strain, suggesting proteases are involved in virulence. These caused histolysis in the insect mid-gut. This suggest that proteases are involved in pathogenesis. During invasion and installation occurs up-regulating of more proteases. Studies suggest that the main function is inhibition hemocyte aggregation and the entrapment of foreign particles by fibers. Moreover, it avoids encapsulation and the deposition of clotting materials, which usually occurs in response to foreign particles. Very important for insect is phenoloxidase cascade, which is influence by sexcreted/secreted products. In vivo experiment demonstrated that beads imbibed by chymotrypsin could prevent hemocyte encapsulation and melanisation. Some of them can also play a role in the diet control or for instance in the interaction with host immune system. The work with them is complicated, because of their distinct activities and presence in mixtures, which is also a main reason why lots of them are not described yet.