Gnotobiological study of infective juveniles and symbionts of Steinernema scapterisci: A model to clarify the concept of the natural occurrence of monoxenic associations in entomopathogenic nematodes.

Gnotobiology of Steinernema scapterisci and bacteriological study of its symbiont confirmed that this nematode harbors a symbiotic species of Xenorhabdus, as do other Steinermena species. Based on phenotypic and 16S rDNA data, this Xenorhabdus strain UY61 could be distinguished from other Xenorhabdus species. Bacteria reported previously as being associated with this nematode and belonging to several other genera were probably contaminating bacteria located in the intercuticular space of the infective juveniles (IJs). These bacteria were detrimental to nematode reproduction in Galleria mellonella. Axenic S. scapterisci and its symbiont Xenorhabdus strain UY61 alone were not pathogenic to G. mellonella. The combination of both partners reestablished the pathogenicity of the complex toward G. mellonella. This combination also gave the best yields of IJs when produced in this insect and in vitro production on artificial diet.