CULTIVATION OF AXENIC HETERORHABDITIS SPP. DAUER JUVENILES AND THEIR RESPONSE TO NONSPECIFIC PHOTORHABDUS-LUMINESCENS FOOD SIGNALS

A method is described for the production of bacteria-free Heterorhabdi tis bacteriophora and H, indica dauer juveniles by culturing these nem atodes. on Photorhabdus luminescens symbionts isolated from H. megidis and from H. bacteriophora, respectively. The nematodes develop and re produce, feeding on the bacterial cells, but the symbionts are not ret ained by the dauer juveniles. Through surface sterilisation of the res ulting dauer juveniles, axenic dauer juveniles could be produced, whic h were used for compatibility tests. The tests showed that H. bacterio phora did not reproduce on the symbionts of H, indica and that H. indi ca did not reproduce on the symbiont isolated from an undescribed Hete rorhabditis species (Q6). Dauer juveniles of Heterorhabditis species s tart development (recover) in response to food signals excreted into t he culture by P. luminescens. The recovery inducing signal may be prod uced 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 becaus e they lack the enzymes needed to digest the bacterial cells. Food sig nals produced by Xenorhabdus species, the symbionts of Steinernema spe cies, do not induce recovery of H. bacteriophora. Currently, bacteria isolated from different Heterorhabditis species are all assigned to th e species P. luminescens. The specificity of the nutritive function su pports the subdivision of the taxon P. luminescens into several specie s.