Around 1974, I started bacteriological studies on the microbiota of EPNs, following the request of my colleague nematologist C. Laumond (INRA Antibes France). I contacted people concerned by this subject that were at this stage the pioneers of the subject, the Prof. Poinar (University of Berkeley, USA), Dr Lysenko bacteriologist of the Czech Invertebrate Pathology laboratory of Prof. Weiser, and the Australian team working on EPNs in CSIRO in Hobart, Drs Akhurst and Bedding. It was the time that the concept of the symbiotic association with a specific bacterium discovered by Prof Poinar named Xenorhabdus, was confirmed and extended to several species of Steinernema by Akhurst (PhD thesis,1982) and, later, species of Heterorhabditis. However, the bacterial species isolated from EPNs were not the same every time. Lysenko found species of Pseudomonas, and from my side, though I found Xenorhabdus every time, I also randomly found Pseudomonadaceae and Enterobacteriaceae (PhD thesis,1983). In that time, the most urgent topic was to develop the taxonomy of the Xenorhabdus in terms of phenotypic and genotypic properties. I engaged in a cooperation with Dr Akhurst to study the specificity of these symbiotic associations in order to define new species of Xenorhabdus for the symbionts of different species of Steinernema (Akhurst and Boemare, Bergey’s Manual Vol. 2, 2005) and to define a new genus, Photorhabdus, removed from Xenorhabdus, for all the symbiont species associated with Heterorhabditis (Boemare and Akhurst, ibid. 2005). The main topics of this talk will develop the results of this very fruitful cooperation.