Metagenomic Profiling Reveals Lignocellulose Degrading System in a Microbial Community Associated with a Wood-Feeding Beetle

Abstract

The Asian longhorned beetle ( Anoplophoraglabripennis ) is an invasive, wood-boring pest that thrives in the heartwood of deciduous tree species. A large impediment faced by A . glabripennis as it feeds on woody tissue is lignin, a highly recalcitrant biopolymer that reduces access to sugars and other nutrients locked in cellulose and hemicellulose. We previously demonstrated that lignin, cellulose, and hemicellulose are actively deconstructed in the beetle gut and that the gut harbors an assemblage of microbes hypothesized to make significant contributions to these processes. While lignin degrading mechanisms have been well characterized in pure cultures of white rot basidiomycetes, little is known about such processes in microbial communities associated with wood-feeding insects. The goals of this study were to develop a taxonomic and functional profile of a gut community derived from an invasive population of larval A . glabripennis collected from infested host trees and to identify genes that could be relevant for the digestion of woody tissue and nutrient acquisition. To accomplish this goal, we taxonomically and functionally characterized the A . glabripennis midgut microbiota through amplicon and shotgun metagenome sequencing and conducted a large-scale comparison with the metagenomes from a variety of other herbivore-associated communities. This analysis distinguished the A. glabripennis larval gut metagenome from the gut communities of other herbivores, including previously sequenced termite hindgut metagenomes. Genes encoding enzymes were identified in the A . glabripennis gut metagenome that could have key roles in woody tissue digestion including candidate lignin degrading genes (laccases, dye-decolorizing peroxidases, novel peroxidases and β-etherases), 36 families of glycoside hydrolases (such as cellulases and xylanases), and genes that could facilitate nutrient recovery, essential nutrient synthesis, and detoxification. This community could serve as a reservoir of novel enzymes to enhance industrial cellulosic biofuels production or targets for novel control methods for this invasive and highly destructive insect.

Gut Microbes Contribute to Nitrogen Provisioning in a Wood-Feeding Cerambycid

“…These results are consistent with another study that detected the presence of microbial urease and of nifH genes from the A. glabripennis larval gut microbial community metagenome (Scully et al 2013). Furthermore, insect endogenous urease and nitrogenase transcripts were not detected in the larval gut of this species (Scully et al 2013).…”

“…Furthermore, insect endogenous urease and nitrogenase transcripts were not detected in the larval gut of this species (Scully et al 2013). Results from A. glabripennis are also consistent with studies that detected the presence of microbial ureC genes in the eggs of the carpenter ant Camponotus floridanus, which harbors the obligate urea-hydrolyzing endosymbiont Blochmannia (Zientz et al 2006).…”

“…Results from A. glabripennis are also consistent with studies that detected the presence of microbial ureC genes in the eggs of the carpenter ant Camponotus floridanus, which harbors the obligate urea-hydrolyzing endosymbiont Blochmannia (Zientz et al 2006). Previous studies on A. glabripennis have shown that the beetle larvae harbor a diverse gut microbial community (Geib et al 2009, Scully et al 2013, including members of the family Enterobacteriaceae, which consist of several nitrogenÞxing and urea-recycling members (in the examples listed above), and these taxa may be contributors to the observed nitrogen cycling in A. glabripennis larvae. Culture-dependent studies to identify some of these taxa more speciÞcally are in progress.…”

Genome of the Asian longhorned beetle (Anoplophora glabripennis), a globally significant invasive species, reveals key functional and evolutionary innovations at the beetle–plant interface

“…Recent insertions have similarly been detected in other arthropod genomes using the DNA-based pipeline [24, 25]. In contrast, the GH HGTs are more ancient insertions that have evolved into functional genes [26–30] (see results from in vitro functional characterization, discussed in section titled Plant cell wall degradation). No microbial scaffolds were found in the A. glabripennis assembly, likely because the tissues used for sequencing (Additional file 1) are not known to be associated with microbes.…”

Gill bacteria enable a novel digestive strategy in a wood-feeding mollusk

“…At least one shipworm species (Lyrodus pedicellatus) has been shown to grow and reproduce normally using wood as its sole particulate food source (3). However, unlike their terrestrial herbivorous and xylophagous counterparts, whose digestive systems contain complex communities of microbes (4)(5)(6)(7)(8)(9), Bankia setacea and several other shipworm species accumulate and digest wood in the cecum ( Fig. 1 A and B), a region of the foregut that is devoid of any conspicuous microbial community (10).…”