| Xylophagous insects are proposed to thrive on nutritionally suboptimal diets through symbiotic associations with microbes that supplement their nutritional requirements, particularly nitrogen (proteins). The wood-feeding Anoplophora glabripennis, harbors a diverse gut microbial community. We investigated the contributions of gut microbiota to larval A. glabripennis metabolic nitrogen requirements through nitrogen fixing and recycling (urea hydrolysis) processes, as well as to essential amino acid (EAA) requirements, using a combination of molecular, functional and stable isotope approaches. Genes and transcripts from bacteria with urease and nitrogen fixation capabilities were detected in A. glabripennis eggs and larvae from naturally infested logs and from larvae reared on artificial diet. Nitrogen fixation and nitrogen recycling were documented in larvae, including incorporation of fixed and recycled nitrogen into insect biomass. Compound-specific isotope analysis of amino acids revealed 15N-routing into essential amino acids of larvae fed 15N-urea diets, and significant gut microbial contributions to essential amino acid carbon backbones in larvae based on 13C fingerprint analyses. Results from this study show that the gut microbiota of A. glabripennis make important contributions to the insect's metabolic nitrogen requirement through nitrogenous waste product recycling and nitrogen fixation. Provisioning of essential amino acids by members of the gut microbiota also support the hypothesis that at least a portion of these symbionts are mutualists. |
