Lignocellulose degradation and gut microbial community composition in the Asian longhorned beetle (Anoplophora glabripennis)

The Asian longhorned beetle (ALB; Anoplophora glabripennis) thrives in an inhospitable environment on an intractable energy source, the inner wood of hardwood trees. This inner wood is high in lignin and heavily cross-linked, making it low in accessible nutrients, including carbohydrates and nitrogen. How this or any other insect is able to grow and develop in living woody tissue is largely unknown but likely requires specific enzymes and biochemical pathways. While insects are not thought to have the ability to fully degrade lignocellulose through endogenous enzymes, microbes present in the gut of insects assist in this process. To better understand this relationship, the gut microbial community of this insect was investigated in detail through multiple populations of the insect on different hosts, as well as over different insect developmental stages. A. glabripennis harbors a broad diversity of bacteria in its gut, some of which likely produce cellulases, xylanases and enzymes able to degrade aromatic compounds, as well as microbes capable of nitrogen fixation. Some of these bacteria are passed during oviposition from the adult, while others are environmentally derived. Also, a fungal species in the Fusarium solani species complex is associated with the gut of this insect. This strain was consistently found in the gut upon examination of several host tree species and different populations of A. glabripennis from different locations. While not a typical wood-rot fungus, this species does produce hydrolases and may have some ability to degrade lignin, but the details of these processes are not known. Lignin degradation in A. glabripennis, as well as the Pacific dampwood termite Zootermopsis angusticollis was demonstrated using tetramethylammonium hydroxide (TMAH) thermochemolysis/GC/MS. Side-chain oxidation, demethylation, and ring hydroxylation were recorded as wood passed through the guts of these insects. This is the first definitive report of lignin degradation by insects. Overall, this research lays the foundation for understanding lignocellulose degradation and gut microbial ecology in A. glabripennis with future studies planned to explore the meta-genome, transcriptome, and proteome of this insect. Potential applications include novel targets for controlling this pest and prospecting for novel biochemical processes and microbes that can be utilized in industrial processes, including cellulosic ethanol production.