Diet and ontogeny drastically alter the larval microbiome of the invertebrate modelGalleria mellonella

Larvae of the greater wax moth (Galleria mellonella) are an emerging animal model to study the innate immune response and biodegradation of plastic polymers. Both of these complex biological processes are likely impacted by the plasticity of host-microbe interactions, which remains understudied in lepidopterans. Consequently, we carried out 16S rRNA sequencing to explore the effect diet (natural, artificial) has on the bacterial assemblages of G. mellonella in different tissues (gut, fat bodies, silk glands) throughout development (eggs, six instar stages, adults). The microbiome was rich in diversity, with Proteobacteria and Firmicutes being the most represented phyla. Contrary to other lepidopterans, G. mellonella appears to possess a resident microbiome dominated by Ralstonia. As larvae progress through development, the bacterial assemblages become increasingly shaped by the caterpillar's diet. In particular, a number of bacteria genera widely associated with the G. mellonella microbiome (e.g., Enterococcus and Enterbacter) were significantly enriched on an artificial diet. Overall, these results indicate that the G. mellonella microbiome is not as simplistic and homogenous as previously described. Rather, its bacterial communities are drastically affected by both diet and ontogeny, which should be taken into consideration in future studies planning to use G. mellonella as model species.