Death Becomes Them: Bacterial Community Dynamics and Stilbene Antibiotic Production in Cadavers of Galleria mellonella Killed by Heterorhabditis and Photorhabdus spp

Insect larvae killed by entomopathogenic nematodes are thought to contain bacterial communities dominated by a single bacterial genus, that of the nematode's bacterial symbiont. In this study, we used next-generation sequencing to profile bacterial community dynamics in greater wax moth (Galleria mellonella ) larvae cadavers killed byHeterorhabditis nematodes and theirPhotorhabdus symbionts. We found that, althoughPhotorhabdus strains did initially displace anEnterococcus- dominated community present in uninfectedG. mellonella insect larvae, the cadaver community was not static. Twelve days postinfection,Photorhabdus shared the cadaver withStenotrophomonas species. Consistent with this result,Stenotrophomonas strains isolated from infected cadavers were resistant toPhotorhabdus- mediated toxicity in solid coculture assays. We isolated and characterized aPhotorhabdus- produced antibiotic fromG. mellonella cadavers, produced it synthetically, and demonstrated that both the natural and synthetic compounds decreasedG. mellonella- associatedEnterococcus growth, but notStenotrophomonas growth,in vitro . Finally, we showed that theStenotrophomonas strains described here negatively affectedPhotorhabdus growthin vitro . Our results add an important dimension to a broader understanding ofHeterorhabditis -Photorhabdus biology and also demonstrate that interspecific bacterial competition likely characterizes even a theoretically monoxenic environment, such as aHeterorhabditis -Photorhabdus -parasitized insect cadaver.IMPORTANCE Understanding, and eventually manipulating, both human and environmental health depends on a complete accounting of the forces that act on and shape microbial communities. One of these underlying forces is hypothesized to be resource competition. A resource that has received little attention in the general microbiological literature, but likely has ecological and evolutionary importance, is dead/decaying multicellular organisms. Metazoan cadavers, including those of insects, are ephemeral and nutrient-rich environments, where resource competition might shape interspecific macrobiotic and microbiotic interactions. This study is the first to use a next-generation sequencing approach to study the community dynamics of bacteria within a model insect cadaver system: insect larvae parasitized by entomopathogenic nematodes and their bacterial symbionts. By integrating bioinformatic, biochemical, and classicin vitro microbiological approaches, we have provided mechanistic insight into how antibiotic-mediated bacterial interactions may shape community dynamics within insect cadavers.