Interaction Between Entomopathogenic Nematode Heterorhabditidoides Rugaoensis And Its Symbiotic Bacteria Serratia Nematodiphila R187 With Immune System Of Adult Drosophila Melanogaster

Entomopathogenic nematodes (EPNs) are parasites which can kill host with the help of symbiotic bacteria in their intestine. The entomopathogenic nematode Heterorhabditidoides rugaoensis is a new species of Rhabditidae. The pathogenic of Heterorhabditidoides rugaoensis is enhanced by its symbiotic bacteria Serratia nematodiphila R187. Up to now, the interaction between complex H. rugaoensis-S. nematodiphila R187 and immune system of insect is not clear.Our research simulate the natural infection environment:infecting the Drosophila melanogaster with symbiotic nematode, feeding the fly with symbiotic bacterial strain and needle-pricking the fly with the symbiotic bacterial strain. The methods were used to make H. rugaoensis-S. nematodiphila R187 infect both wildtype and mutant type of Drosophila melanogaster successfully in their intestine and hemocoel. Fly surival rate, the symbiotic bacterial colony combined with Q-PCR detection of expression of the two antimicrobial peptides regulated by Imd pathway and Toll pathway were analyzed to recover the interaction between H. rugaoensis-S. nematodiphila R187 and D. melanogaster.The infection of H. rugaoensis with its symbiotic bacterium could activate the Toll and Imd pathway, which was same as the infection of symbiotic bacteria in flies’ intestine and hemocoel. The entomopathogenic nematode infection and instetine infection of the symbiotic bacterium to flies showed that the expression of Diptericin was up-regulation after 24 h because of phagocytosis by intestinal epithelial cell. Wildtype, FADD mutant and Dif mutant of fly had the same surival rate when fed on Serratia nematodiphila R187, which suggested that Serratia nematodiphila R187 may release toxin leading to the fly death and except for the intestine immune response of fly. In hemocoel infection, Diptericin and Drosomycin were expressed in a high level, both in wildtype or in mutant fly, the expression level of Diptericin and Drosomycin in mutant fly was different from wildtype for the defective immune system. According to the surival rate, Fadd mutant fly was more sensitive to S. nematodiphila R187 in contrast to Dif mutant fly, which suggested that Imd pathway can defend symbiotic bacteria more efficently.