Functional metagenomic and transcriptomic profiling of the asian longhorned beetle (Cerambycidae: Anoplophora glabripennis) midgut: Insights into nutritional ecology

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, wood polysaccharides, including cellulose and hemicellulose, are inherently difficult to digest and require a suite of enzymes for efficient degradation.  Access to polysaccharides and nutrients is further limited by the presence of lignin, a structural biopolymer that contains twelve types of chemical bonds and is highly resistant to degradation.  Wood is also lacking in essential amino acids, vitamins, proteins, sterols, and fatty acids. 

While transcriptome profiling revealed that ALB endogenously produces a number of glycoside hydrolases that can facilitate digestion of major hardwood polysaccharides and lignin, we hypothesize that cooperation with microbial enzymes enhances digestive and metabolic processes and facilitates essential nutrient acquisition.  Shotgun metagenomic profiling of gut microbes revealed a taxonomically diverse community with the metabolic capacity to degrade cellulose and hemicellulose, disrupt the major linkages in the lignin polymer, convert xylose sugars that dominate hardwood hemicellulose into compounds that can be utilized by ALB, fix atmospheric nitrogen, and recycle nitrogenous waste products.  Thus, we hypothesize that the metabolic potential of the gut community enhances ALB’s endogenous metabolic capabilities, complements its deficiencies, and encodes more extensive suites of enzymes, enabling ALB to complete development in a broad host range.