Microbial community pattern after infections of Tenebrio molitor with entomopathogenic nematodes associated with Xenorhabdus.

The host and/or vector microbiota positively or negatively impacts pathogens and thus change the consequences of infections. To further understand these effects, this study aims at describing bacterial environment, in which stands the pathogen before reassociation with its vector. We focused on the Steinernema-Xenorhabdus pairs. The entomopathogenic bacterial symbiont Xenorhabdus (Enterobacteriaceae) is transmitted into soil-dwelling insect larvae by infective juveniles (IJs) of the nematode Steinernema. In order to mimic soil-dwelling insects, we used Tenebrio molitor larvae that were previously acclimated to soil. We first assessed mortality and parasitic success of three Steinernema-Xenorhabdus pairs. The three pairs do induce lethal infection on soil-acclimated T. molitor larvae. In order to describe bacterial communities co-existing with Xenorhabdus at the end of insect infectious process, we underwent V3-V4 16S rRNA metabarcoding analysis of bacterial community inside insects cadaver ten days after infection. We showed that infection modifies the bacterial community, but an important inter-individual variability remains. More surprisingly, even with highly lethal Steinernema-Xenorhabdus pairs, the symbiont rarely dominates the bacterial communities inside insects cadaver. These bacterial communities are generally typed by one or two mains taxa, which raises question about the reassociation of Xenorhabdus to its specific vector and about Xenorhabdus transmission.