Unlocking the potential of insect and ruminant host symbionts for recycling of lignocellulosic carbon with a biorefinery approach: a review

Abstract

Uprising fossil fuel depletion and deterioration of ecological reserves supply have led to the search for alternative renewable and sustainable energy sources and chemicals. Although first generation biorefinery is quite successful commercially in generating bulk of biofuels globally, the food versus fuel debate has necessitated the use of non-edible feedstocks, majorly waste biomass, for second generation production of biofuels and chemicals. A diverse class of microbes and enzymes are being exploited for biofuels production for a series of treatment process, however, the conversion efficiency of wide range of lignocellulosic biomass (LCB) and consolidated way of processing remains challenging. There were lot of research efforts in the past decade to scour for potential microbial candidate. In this context, evolution has developed the gut microbiota of several insects and ruminants that are potential LCB degraders host eco-system to overcome its host nutritional constraints, where LCB processed by microbiomes pretends to be a promising candidate. Synergistic microbial symbionts could make a significant contribution towards recycling the renewable carbon from distinctly abundant recalcitrant LCB. Several studies have assessed the bioprospection of innumerable gut symbionts and their lignocellulolytic enzymes for LCB degradation. Though, some reviews exist on molecular characterization of gut microbes, but none of them has enlightened the microbial community design coupled with various LCB valorization which intensifies the microbial diversity in biofuels application. This review provides a deep insight into the significant breakthroughs attained in enrichment strategy of gut microbial community and its molecular characterization techniques which aids in understanding the holistic microbial community dynamics. Special emphasis is placed on gut microbial role in LCB depolymerization strategies to lignocellulolytic enzymes production and its functional metagenomic data mining eventually generating the sugar platform for biofuels and renewable chemicals production.

Lignocellulose degradation in Protaetia brevitarsis larvae digestive tract: refining on a tightly designed microbial fermentation production line

“…In nature, scarab larvae such as PBL are attracted to carbon dioxide (CO 2 ) [ 54 ], which drives saprophagous PBL to feed on decaying organic matter. This feeding is beneficial to many aspects of lignocellulose degradation in the PBL holobiont: (a) the PBL chews and crushes lignocellulosic biomass, which may reduce recalcitrance of the substrate and allow PBL to achieve greater lignocellulose degradation efficiency [ 55 ]; (b) the PBL ingests a large number of lignocellulose-decomposing bacteria from the decaying organic matters, most of which will be killed and hydrolyzed in the midgut, providing nutrients for PBL development [ 56 ], while some surviving from the midgut will contribute to the hindgut lignocellulosic bacteria flora [ 57 ]. Beyond feeding habits, a strong alkaline environment in the PBL midgut facilitates the solubility of organic polymers.…”

Enrichment of Anaerobic Microbial Communities from Midgut and Hindgut of Sun Beetle Larvae (Pachnoda marginata) on Wheat Straw: Effect of Inoculum Preparation

“…Consequently, alkaline pretreatment appears as a good approach for application in anaerobic systems, since in natural systems, lignin can be degraded efficiently only in the presence of oxygen. Unfortunately, it is still a great biotechnological challenge to perfectly mimic the physicochemical conditions of the larvae's gut in artificial systems and achieve the same lignocellulosic biomass conversion [85], which could lead to an increase in the either production of carboxylates or biogas.…”

Could termites be hiding a goldmine of obscure yet promising yeasts for energy crisis solutions based on aromatic wastes? A critical state-of-the-art review

“…Termites have a high capacity for biomass degradation and may thus contribute to global carbon recycling. This remarkable ability is largely attributed to the metabolic performance of their "gut digestome", which includes intestinal symbiotic microorganisms like bacterial, archaeal, yeast, or other eukaryotic symbionts, as well as the abundance of species, enzymes, and genes found in the termite's digestive tract [ 22 , 23 ]. However, their highly specialized gut systems remain poorly understood in terms of their unique symbiont functions and their potential applications in biotechnology and other relevant fields, particularly for the yeast symbionts.…”