Morphophysiological study of digestive system litter-feeding termite Cornitermes cumulans (Kollar, 1832)

Abstract

Termites are the major decomposers of lignocellulosic biomass on Earth and are commonly considered as biological reactor models for lignocellulose degradation. Despite their biotechnological potential, few studies have focused on the morphophysiological aspects of the termite digestive system. We therefore analyze the morphology, ultrastructure and gut luminal pH of the digestive system in workers of the litter-feeding termite Cornitermes cumulans (Blattodea: Termitidae). Their digestive system is composed of salivary glands and an alimentary canal with a pH ranging from neutral to alkaline. The salivary glands have an acinar structure and present cells with secretory characteristics. The alimentary canal is differentiated into the foregut, midgut, mixed segment and hindgut, which comprises the ileum (p1), enteric valve (p2), paunch (p3), colon (p4) and rectum (p5) segments. The foregut has a well-developed chewing system. The midgut possesses a tubular peritrophic membrane and two cell types: digestive cells with secretory and absorptive features and several regenerative cells in mitosis, both cell types being organized into regenerative crypts. The mixed segment exhibits cells rich in glycogen granules. Hindgut p1, p4 and p5 segments have flattened cells with a few apical invaginations related to mitochondria and a thick cuticular lining. Conversely, the hindgut p3 segment contains large cuboid cells with extensive apical invaginations associated with numerous mitochondria. These new insights into the morphophysiology of the digestive system of C. cumulans reveal that it mobilizes lignocellulose components as a nutritional source by means of a highly compartmentalized organization with specialized segments and complex microenvironments.

De novo transcriptome assembly of the bamboo snout beetle Cyrtotrachelus buqueti reveals ability to degrade lignocellulose of bamboo feedstock

“…This insect damages bamboo shoots via both its piercing–sucking mode of feeding and egg-laying [ 28 ]. On the basis of previous research on termites and other beetles that utilise lignocellulosic biomass [ 29 – 34 ], in the present study, we used RNA sequencing and quantification of lignocellulolytic enzyme activity to explore the possibility of bioconversion of lignocellulosic biomass of bamboo feedstock by C. buqueti .…”

The relationship between oxidant levels and gut physiology in a litter-feeding termite

“…In the hindgut, p1 compartment showed no levels of oxidants and low densities of Archaea and Eubacteria, which might be associated with the extremely alkaline condition of this segment’s lumen 37 . Low oxidant levels in the hindgut p3 segment together with high SOD and GPX transcript levels and enzymatic activities probably account for the development of a propitious environment for the greatest abundance of Eubacteria.…”

“…While there are some studies describing the organization of the termite digestive system into different physicochemical microenvironments 37,42–49 , little is known about oxidant properties of their gut compartments. It has been proposed that non-enzymatic oxidative mechanisms might be involved in the digestive physiology of the termite guts 17,18 , either by creating an oxidative environment required for polyphenol-rich diet digestion or as a byproduct of the digestive process.…”

“…High levels of antioxidant enzymes (SOD and GPX) in the foregut and hindgut compartments probably are involved in the protection of the insect gut and its microbiota against potential oxidative injuries. Additionally, these compartments have cuticular layers protecting the luminal surface of the epithelial cells from abrasive and chemical damage 37 . On the contrary, high levels of oxidants in the midgut (an endodermic tissue devoid of cuticular layers) occurred together with low SOD and GPX transcript levels and enzymatic activities, where the cells seem to be more susceptible to oxidative damage.…”

“…It digests lignocellulose from litter and ingests soil for nest building 36 . Apart from the structural organization of the digestive system 37 and gut microbiota composition 38,39 , there are no other descriptive reports of the gut physiology in C . cumulans .…”