Cultivation of axenic Heterorhabditis spp. dauer juveniles and their response to non-specific Photorhabdus luminescens food signals

A method is described for the production of bacteria-free Heterorhabditis bacteriophora and H. indica dauer juveniles by culturing these nematodes on Photorhabdus luminescens symbionts isolated from H. megidis and from H. bacteriophora, respectively. The nematodes develop and reproduce, feeding on the bacterial cells, but the symbionts are not retained by the dauer juveniles. Through surface sterilisation of the resulting dauer juveniles, axenic dauer juveniles could be produced, which were used for compatibility tests. The tests showed that H. bacteriophora did not reproduce on the symbionts of H. indica and that H. indica did not reproduce on the symbiont isolated from an undescribed Heterorhabditis species (Q6). Dauer juveniles of Heterorhabditis species start development (recover) in response to food signals excreted into the culture by P. luminescens. The recovery inducing signal may be produced by strains on which the nematode cannot reproduce. In cultures of such incompatible bacterial strains, developing dauer juveniles take up the bacteria in the intestine but die after 3 days, probably because they lack the enzymes needed to digest the bacterial cells. Food signals produced by Xenorhabdus species, the symbionts of Steinernema species, do not induce recovery of H. bacteriophora. Currently, bacteria isolated from different Heterorhabditis species are all assigned to the species P. luminescens. The specificity of the nutritive function supports the subdivision of the taxon P. luminescens into several species.