gut microbiome, Lepidoptera, metabolic interaction,
stable isotope labelling, Enterococcus
The gut microbiota is of crucial importance for the host with considerable metabolic activity. Although Lepidoptera is one of the largest insect orders and a primary group of phytophagous agricultural pests, little is known about the microbes associated with them. We have made efforts to comprehensively characterize the gut microbiota in different lepidopteran model organisms (Spodoptera littoralis and Helicoverpa armigera) and provide some light into the potential metabolic functions of the core components inside the host. The gut microbiota profile of the two species is very similar regarding high abundant bacterial families that are dominated by Firmicutes and Proteobacteria. Different bacteria colonize specialized niches within the gut. A core community, consisting of Pantoea, Enterococci, Lactobacilli and Clostridia, is revealed in the insect larvae. These bacteria are constantly present in the digestion tract at relatively high frequency despite that the developmental stage and the diet have some impacts on shaping the bacterial communities. Some low-abundant species might become dominant upon loading external disturbances; the core community, however, did not change significantly. Clearly, the insect gut selects for particular bacterial phylotypes as the indigenous community, which may contribute to the host fitness. Furthermore, the components’ metabolic activity was measured in S. littoralis by using a refined Pyro-SIP approach. With 13C glucose as the trophic link, Pyro-SIP revealed that the gut microbiota co-develops with the host, both metabolic activity and composition shifting throughout larval stages. Bacteria from the Clostridiaceae and Enterobacteriaceae families are particularly active in the early instar, which are well-known plant biomass degraders and likely the core functional populations linked to nutritional upgrading. Enterococcaceae is highly active in the late instar. On the grounds that enterococci are maintained in a biofilm-like structure on the gut epithelium and that the isolated strains efficiently produce a mixture of antibiotic regents, Enterococcus is suggested to be a defensive mutualist which helps the host resist potentially harmful bacteria from outside. This pilot study shows that Pyro-SIP can rapidly gain insight into the microbiota’s metabolic activity with high resolution and high precision, which sets the stage for future studies on the targeted metabolic pathway, for instance, labeling plant defense compounds to assess active bacteria involved in the host detoxification process. With the development of such new approaches, the role of lepidopteran gut microbiota will become more apparent than currently.