Functional metagenomic profiling of Asian longhorned beetle (Anoplophora glabripennis) microbiota reveals important contributions to digestive physiology

The Asian longhorned beetle (ALB) is a destructive, wood-boring pest with a broad host range that thrives in the heartwood of healthy deciduous trees. Despite its ability to enjoy a broad host range, ALB must overcome a number of challenges to subsist in heartwood, which is devoid of easily accessible nutrients. For example, glucose in wood is present as cellulose and hemicellulose, which are inherently difficult to digest, requiring a suite of enzymes for efficient degradation. Access to these polysaccharides is further limited by the presence of a recalcitrant lignin barrier, a structural biopolymer that contains twelve types of chemical bonds and is especially resistant to degradation. Wood is also lacking in essential amino acids, vitamins, nitrogen-containing compounds, sterols, and fatty acids.

The ALB gut harbors a phylogenetically diverse microbial community that likely contributes to digestion of intractable compounds and augments the nutritional content of the beetle’s diet. To assess the metabolic potential of these microbiota, we performed shotgun metagenomic sequencing of gut microbial DNA and detected an abundance of genes associated with polysaccharide digestion, including complete suites of microbial-derived cellulase and hemicellulase enzyme complexes. Furthermore, a substantial percentage of genes were associated with amino acid synthesis, indicating that gut microbes may be provisioning ALB with essential amino acids. In addition, we found genes associated with oxidative degradation of small lignin subunits, vitamin biosynthesis, sterol and fatty acid production, and nitrogen fixation, thus demonstrating that the gut microbiota are physiologically capable of helping ALB overcome its digestive and nutritional challenges.