Fig. 1

Flow diagram of the method for obtaining axenic nematodes. Xenorhabdus nematophila ΔrpoS mutant bacteria are grown overnight and then subcultured before plating on oily agar plates containing antibiotics. Surface-sterilized Steinernema carpocapsae nematodes are transferred to the plates covered by the mutant bacteria and after 3–4 weeks infective juvenile progeny are collected in water-traps. These steps consist the first round (Round 1) of the method. The entire procedure is repeated (Round 2) and the newly emerged nematodes are tested for the presence or absence of mutualistic X. nematophila bacteria