38th Annual Meeting of the Society for Invertebrate Pathology

Photorhabdus is a genus of entomopathogenic, gram-negative bacteria normally found colonising the gut of a specialised stage of the nematode Heterorhabditis called the infective juvenile (IJ). The IJ is a free-living stage of the nematode that seeks out and infects insect larvae. The Photorhabdus are released from the IJ into the insect hemolymph where the bacteria rapidly grow and the insect dies 48-72h after the initial infection. The nematode then grows and reproduces in the insect cadaver by feeding on the Photorhabdus bacterial biomass. After several generations the nematodes develop into IJs and the Photorhabdus bacteria re-colonise the nematode gut. During this life cycle the nematode relies on the bacteria for nutrients and in this study we show that iron acquisition by Photorhabdus plays a key role during the course of the tripartite bacteria-nematode-insect interaction. Therefore, during growth in the insect, Photorhabdus must accumulate sufficient iron from the insect tissues to satisfy the nutritional requirements of the nematodes. In addition, we present evidence suggesting that the stilbene antibiotic produced by Photorhabdus may also serve as a signal to control nematode development. Therefore, as is the case in other mutualistic relationships, the interaction between Photorhabdus and its nematode host involves the exchange of nutrients and signals.