Culture dependent and independent methods were used to exhaustively describe the bacterial microbiota which is associated to entomopathogenic nematodes. The role of this microbiota in the nematode life cycle was investigated, e.g. their insecticidal performances and theit potential to produce antimicrobial compounds.

Entomopathogenic nematodes from the genus Steinernema are used in biological control of insect pests. The free form of the nematode (infective juvenile) is in closed symbiotic association with the intestinal bacteria Xenorhabdus (Enterobacteriaceae). In the well-studied Steinernema carpocapsae - Xenorhabdus nematophila couple, it was largely shown that the bacterial symbiont played an important role in the death of the insect and in the elimination of the microbial competitors inside the insect cadaver. However, in addition to symbiotic bacteria, other cultivable bacteria have been regularly isolated from infective juveniles nematodes.In this study,we used both culture-dependent and multigenic metabarcoding methods to obtain a comprehensive survey of S. carpocapsae bacterial microbiota. We used two markers, the V3-V4 region of the 16S rRNA gene and a region of the rpoB gene, for which a database was built. We identified a core-microbiota of about 10 OTUs that were present in more than 70% of the samples. Representative bacterial strains of the core-microbiota were tested for their insecticidal performances and their ability to produce antimicrobial molecules.