Structural basis of lignocellulose deconstruction by the wood-feeding anobiid beetle Nicobium hirtum

Abstract

The details of the lignocellulose deconstruction processes in the digestive systems of wood-feeding insects remain elusive. This study aimed to examine the biochemical conversion of lignocellulose in the digestive system of a wood-feeding anobiid beetle, Nicobium hirtum, one of the most important pests of wooden products in Japan. To this end, N. hirtum larvae were fed with Japanese red pine (softwood) and Japanese beech (hardwood) sapwood diets, as well as an artificial diet containing Shorea wood (hardwood) sapwood sawdust. The structural differences between the original and digested (feces) lignocellulose samples were examined using wet-chemical and two-dimensional (2D) nuclear magnetic resonance (NMR) methods. Cellulose and hemicelluloses, especially mannan in the softwood diet, were preferentially degraded over lignin in the larval digestive system. As a result, lignin was enriched in the digested lignocellulose residues. Lignin compositional analyses based on thioacidolysis and 2D NMR determined that the proportions of oxidized lignin aromatic units were notably increased after digestion. Further, the 2D NMR analyses revealed the accumulation of aldehyde and hydroxypropiovanillone/syringone end-unit structures in lignin, indicating that oxidative and/or reductive modifications of lignin polymers occur in the larval digestive system. Such structural alterations of lignin may facilitate the dissociation of the lignin barrier, thereby liberating polysaccharides for subsequent enzymatic conversion for assimilation and energy.

A review of the entomofauna associated with decaying cacti in New World deserts

“…Cellulose digestion and lignin degradation in insects have been widely studied, mainly oriented toward understanding the role of symbionts or independence of symbionts (Martin et al 1991, Slaytor 1992, Geib et al 2008). Previous studies have shown that polysaccharides (cellulose and hemicelluloses) were preferentially degraded over lignin polymers in lignocellulose-feeding insects, remaining intact in the digestive residues (Krishanti et al 2022). Therefore, it is essential to investigate in cactus wood types (fibrous with more lignin, nonfibrous, with more cellulose, or mixed) the types of insect–microbe interactions by which insects digest lignocelluloses compared to interactions in trees with pycnoxylic wood (cellulose 50%, lignin 25%, and hemicellulose 25%) (Pettersen 1984).…”