The nematobacterial complex Heterorhabditis Photorhabdus as infection model for Drosophila immunity
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| Year of publication | 2009 |
| Type | Conference abstract |
| MU Faculty or unit | |
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| Description | Entomopathogenic nematodes (EPNs) of the genera Heterorhabditis and Steinernema are obligate and lethal insect parasites, in recent years they have been used increasingly as biological control agents for pest insects. Animals from the third developmental stage of nematodes are called dauer juvenile (DJ) or infective juveniles (IJ). IJs occur free living in the soil and are capable of seeking out hosts and penetrate them through either the cuticle or natural orifices. EPNs are symbiotically associated with bacteria of either of the genera Photorhabdus and Xenorhabdus. The bacterial symbionts are essential to kill the insect host (usually within 24-48 hours) and to digest host tissues. Drosophila larvae are more resistant to nematode infection than Galleria mellonella where all larvae can be killed with low nematode dose. The tripartite model (Drosophila, nematodes, bacteria) was recently established by Hallem el al. (2007); we used their modified method to optimize conditions for infection. We used the entomopathogenic nematode Heterorhabditis bacteriophora for three main reasons: 1) this nematode is a natural invasive insect pathogen, thus larvae are infected in a much more reproducible way than by any artificial injection; 2) the infection includes induction of septicemia due to the massive release of the nematodes symbiotic bacteria, which are essential for the nematodes success as an entomophathogen; and 3) although both the Drosophila Toll and imd pathway are induced after infection with H. bacteriophora, it had previously been shown that survival of larvae after nematode infection was unaffected by mutations in either of them. This suggests that previously uncharacterized pathways are involved in surviving infection by the nematodes. Different mutants or RNAi lines of Drosophila with block in clotting or immune system were used to show functional importance of the pathways studied. Our experiments shows that compared to control animals imd, Hml or Bc mutant larvae have similar viability after infection. But surprisingly double mutants imd/Bc as well as imd/Bc/Hml triple mutants show significantly higher mortality suggesting that phenoloxidase cooperate with immunodeficiency pathway in the response to nematobacterial complex. To test the role of transglutaminase activity in innate immunity, we infected normal and TG knockdown Drosophila larvae and followed their survival after infection. Similarly, transglutaminase-knockdown lines showed increased mortality at all time points studied, lending strong support to the requirement for transglutaminase in immune function and survival after infection. To conclude, EPNs are natural very sensitive infection model which can be modified by medium used, nematode dose, nematode specie or temperature, thus it brings tools for many applications in Drosophila experiments. |
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