Lignocellulose Digestion Research Articles

Facilitated lignocellulosic biomass digestibility in anaerobic digestion for biomethane production: microbial communities' structure and interactions

AbstractLignocellulosic biomass is a highly available and suitable candidate for biogas/biomethane production. However, high concentration of recalcitrant lignin is the major obstacle in successful anaerobic digestion (AD). The main aim of this review is to highlight the applications and challenges of lignocellulosic biomass in AD from the recent reports. Potential approaches to improve instabilities in mesophilic AD process (such as microbial communities' development, co‐digestion, biofilm carrier's addition, and essential nutrients supplement) were also reported. This review goes one more step deeper to discuss the key microbes involved in lignocellulosic biomass degradation. Biofilm carriers provide attached growth systems for microbes in AD and acts as redox mediators to accelerate the biotransformation of recalcitrant pollutants. Addition of nanoparticles (NPs) stimulate Firmicutes, Bacteroidetes, Methanosaeta, Methanobacterium, and Methanosarcina population which further improve biomethanation. The comprehensive study of these proposed strategies and microbial stimulation through additives would make the lignocellulosic biomethanation more feasible. © 2021 Society of Chemical Industry (SCI).

Role of Microbial Biomechanics in Composting with Special Reference to Lignocellulose Biomass Digestion

Biomass transformation of lignocellulose into compost offers ‘green’ technology for sustainable agricultural development. So far, biomass conversion into compost outweighs fossil resources and other conversational techniques due to the low production cost and environmental pollution reduction. Although composting has aesthetically been resorted to in the digestibility of lignocellulose biomass, its realization has keenly been directed towards adding chemical reagents. However, inclining massively to this treatment instigated research bias as microorganisms’ biomass digestibility remains mostly inadequate. Besides, proliferated growth and activities of microorganisms native to lignocellulose biomass are usually disrupted by chemical treatment. The microbial flora (fungi, bacteria, actinomycetes, archaea, and yeast) involved in composting synthesizes complex biocatalysts (enzymes) that are crucial for solubilizing the biopolymers of lignocellulose materials at a density of 1012 cells g-1. Filamentous fungi are by far excellent degraders of lignocellulose in nature. To adequately ensure sustainable lignocellulose digestibility, microbial engineers must subject research studies to surpassing conditions (feedstock formulation and management processes) suitable for inducing ligninolytic, cellulolytic, and hemicellulolytic enzymes. Hence, the state-of-the-art-method of this review provides insights that relate to mechanisms of microbial reactions on the digestibility of lignocellulose biomass during composting.

Characterization of new cristamonad species from kalotermitid termites including a novel genus, Runanympha

Cristamonadea is a large class of parabasalian protists that reside in the hindguts of wood-feeding insects, where they play an essential role in the digestion of lignocellulose. This group of symbionts boasts an impressive array of complex morphological characteristics, many of which have evolved multiple times independently. However, their diversity is understudied and molecular data remain scarce. Here we describe seven new species of cristamonad symbionts from Comatermes, Calcaritermes, and Rugitermes termites from Peru and Ecuador. To classify these new species, we examined cells by light and scanning electron microscopy, sequenced the symbiont small subunit ribosomal RNA (rRNA) genes, and carried out barcoding of the mitochondrial large subunit rRNA gene of the hosts to confirm host identification. Based on these data, five of the symbionts characterized here represent new species within described genera: Devescovina sapara n. sp., Devescovina aymara n. sp., Macrotrichomonas ashaninka n. sp., Macrotrichomonas secoya n. sp., and Macrotrichomonas yanesha n. sp. Additionally, two symbionts with overall morphological characteristics similar to the poorly-studied and probably polyphyletic ‘joeniid’ Parabasalia are classified in a new genus Runanympha n. gen.: Runanympha illapa n. sp., and Runanympha pacha n. sp.

Metabolic Potential for Reductive Acetogenesis and a Novel Energy-Converting [NiFe] Hydrogenase in Bathyarchaeia From Termite Guts - A Genome-Centric Analysis.

Symbiotic digestion of lignocellulose in the hindgut of higher termites is mediated by a diverse assemblage of bacteria and archaea. During a large-scale metagenomic study, we reconstructed 15 metagenome-assembled genomes of Bathyarchaeia that represent two distinct lineages in subgroup 6 (formerly MCG-6) unique to termite guts. One lineage (TB2; Candidatus Termitimicrobium) encodes all enzymes required for reductive acetogenesis from CO2 via an archaeal variant of the Wood–Ljungdahl pathway, involving tetrahydromethanopterin as C1 carrier and an (ADP-forming) acetyl-CoA synthase. This includes a novel 11-subunit hydrogenase, which possesses the genomic architecture of the respiratory Fpo-complex of other archaea but whose catalytic subunit is phylogenetically related to and shares the conserved [NiFe] cofactor-binding motif with [NiFe] hydrogenases of subgroup 4 g. We propose that this novel Fpo-like hydrogenase provides part of the reduced ferredoxin required for CO2 reduction and is driven by the electrochemical membrane potential generated from the ATP conserved by substrate-level phosphorylation; the other part may require the oxidation of organic electron donors, which would make members of TB2 mixotrophic acetogens. Members of the other lineage (TB1; Candidatus Termiticorpusculum) are definitely organotrophic because they consistently lack hydrogenases and/or methylene-tetrahydromethanopterin reductase, a key enzyme of the archaeal Wood–Ljungdahl pathway. Both lineages have the genomic capacity to reduce ferredoxin by oxidizing amino acids and might conduct methylotrophic acetogenesis using unidentified methylated compound(s). Our results indicate that Bathyarchaeia of subgroup 6 contribute to acetate formation in the guts of higher termites and substantiate the genomic evidence for reductive acetogenesis from organic substrates, possibly including methylated compounds, in other uncultured representatives of the phylum.

Diet, habitat environment and lifestyle conversion affect the gut microbiomes of giant pandas

Gut microbiota (GM) are important for the health of giant pandas (GPs), in addition to the utilization of bamboo in their diets. However, it is not fully understood how diet, habitat environment and lifestyle contribute to the composition of GM in GP. Consequently, we evaluated how dietary changes, habitat environment conversions and lifestyle shifts influence the GM of GPs using high-throughput sequencing and genome-resolved metagenomics. The GM of GPs were more similar when their hosts exhibited the same diet. High fiber diets significantly increased the diversity and decreased the richness of gut bacterial communities alone or interacted with the age factor (p < 0.05). The abundances of Streptococcus, Pseudomonas, Enterococcus, Lactococcus, Acinetobacter, and Clostridium significantly increased during diet conversion process (Non-parametric factorial Kruskal-Wallis sum-rank test, LDA > 4). Reconstruction of 60 metagenome-assembled-genomes (MAGs) indicated that these bacteria were likely responsible for bamboo digestion via gene complements involved in cellulose, hemicellulose, and lignin degradation. While habitat environment may play a more important role in shaping the GM of GP, lifestyle can also greatly affect bacterial communities. The GM structure in reintroduced GPs notably converged to that of wild pandas. Importantly, the main bacterial genera of wild GPs could aid in lignin degradation, while those of reintroduced GPs were related to cellulose and hemicellulose digestion. Streptococcus, Pseudomonas, Enterococcus, Lactococcus, Acinetobacter, and Clostridium may contribute to lignocellulose digestion in GP. The results revealed that diet conversion, habitat environment and lifestyle could remarkably influence the GM of GP. In addition, results suggested that increasing the ability of lignin degradation with GM may aid to change the GM of reintroduced pandas to resemble those of wild pandas.

Features correlated to improved enzymatic digestibility of corn stover subjected to alkaline hydrogen peroxide pretreatment

As one of the leading pretreatment approaches, alkaline hydrogen peroxide (AHP) pretreatment can enhance the enzymatic digestibility of lignocellulose significantly. In this study, the glucan conversion of AHP pretreated corn stover (CS) without and with water-wash were 28.4% and 50.0% higher than that of raw material, respectively. In order to systematically understand its mechanism, analyses of the features of AHP pretreated and raw CS, such as specific surface area, crystallinity, zeta potential, water holding capacity and swelling capacity and others were performed. The weight-average molecular weight (Mw) of the sugars in the hydrolysate and the particle size distribution of the hydrolysis residue were also analyzed. These results explained why AHP-CS was more conducive to enzymatic hydrolysis. The deeper reason was that the removal of lignin and the destruction of hydrogen bonds within cellulose and hemicellulose increased the accessibility of cellulose and reduced the non-productive adsorption of cellulase, which significantly improved the enzymatic digestibility.

A Century of Synergy in Termite Symbiosis Research: Linking the Past with New Genomic Insights.

Termites have long been studied for their symbiotic associations with gut microbes. In the late nineteenth century, this relationship was poorly understood and captured the interest of parasitologists such as Joseph Leidy; this research led to that of twentieth-century biologists and entomologists including Cleveland, Hungate, Trager, and Lüscher. Early insights came via microscopy, organismal, and defaunation studies, which led to descriptions of microbes present, descriptions of the roles of symbionts in lignocellulose digestion, and early insights into energy gas utilization by the host termite. Focus then progressed to culture-dependent microbiology and biochemical studies of host-symbiont complementarity, which revealed specific microhabitat requirements for symbionts and noncellulosic mechanisms of symbiosis (e.g., N2 fixation). Today, knowledge on termite symbiosis has accrued exponentially thanks to omic technologies that reveal symbiont identities, functions, and interdependence, as well as intricacies of host-symbiont complementarity. Moving forward, the merging of classical twentieth-century approaches with evolving omic tools should provide even deeper insights into host-symbiont interplay.

Enhanced biomethane production by 2-stage anaerobic co-digestion of animal manure with pretreated organic waste

Anaerobic co-digestion (AD) of different organic wastes is a promising technique to enhance clean energy (bioenergy) and manure (slurry) production, reducing stress on the environment. This is an experimental study aimed to investigate 2-stage co-digestion of pretreated organic wastes mixed with fresh animal manure (BD) and digester’s operation conditions (digester temperature and pH) to enhance biomethane production. To increase lignocellulose digestibility and biomethane (BM) production, fruit + vegetable waste (FVW) and corn stalks + wheat straw (CR) in ratio (1:1), respectively, were pretreated with inoculum taken from an anaerobic digester of poultry manure at 35 °C. This AD experiment was performed in a fixed dome biodigester with volumetric capacity of 2.3 m3. Biomethane potential (BMP) tests were conducted for biomass treatments and inoculum used (T1, T2, Ti) at 35 °C. In this study, the temperature of biodigester material was measured in mesophilic (30–40°C) and thermophilic (40–50°C) ranges and pH of fresh feed and slurry feed digesters was in optimum methane production range (7.01–7.52). The total daily methane productions from T1 and T2 were 125.13 ml/g VS and 104.89 ml/g VS in mesophilic range (30–40°C) while these values were 148.41 ml/g VS and 132.74 ml/g VS in mesophilic range (40–50°C), respectively. The 2nd stage digestion of slurry from fresh feed digester added 39–45% and 35–38% more methane production in T1 and T2 respectively. On calibration with BMP tests, experimental data have shown the synergetic effect on methane production and its thermal characteristics promoted by co-digestion of pretreated organic waste and BD. The economic and feasibility analysis proved the biomass co-digestion project viable and adoptable with positive (5.39 $) net return value (NRV), 2.92 years payback time (PBT), and 1.34 benefit cost ratio (BCR).

Metagenomics approach to identify lignocellulose-degrading enzymes in the gut microbiota of the Chinese bamboo rat cecum

Abstract Background Lignocellulose is considered a renewable organic material, but the industrial production of biofuel from lignocellulose is challenging because of the lack of highly active hydrolytic enzymes. The guts of herbivores contain many symbiotic microorganisms that have evolved to hydrolyze plant lignocellulose. Chinese bamboo rats mainly consume high-fiber foods, indicating that some members of the intestinal tract microbiota digest lignocellulose, providing these rats with the energy required for growth. Results Here, we used metagenomics to analyze the diversity and functions of the gut microbiota in Chinese bamboo rats. We identified abundant populations of lignocellulose-degrading bacteria, whose main functions involved carbohydrate, amino acid, and nucleic acid metabolism. We also found 587 carbohydrate-active enzyme genes belonging to different families, including 7 carbohydrate esterase families and 21 glycoside hydrolase families. The glycoside hydrolase 3, glycoside hydrolase 1, glycoside hydrolase 43, carbohydrate esterase 4, carbohydrate esterase 1, and carbohydrate esterase 3 families demonstrated outstanding performance. Conclusions The microbes and enzymes identified in our study expand the existing arsenal of proficient degraders and enzymes for lignocellulosic biofuel production. This study also describes a powerful approach for targeting gut microbes and enzymes in numerous industries. How to cite: Bai D, Lin X, Hu Y, et al. Metagenomics approach to identify lignocellulose-degrading enzymes in the gut microbiota of the Chinese bamboo rat cecum. Electron J Biotechnol 2021;50. https://doi.org/10.1016/j.ejbt.2020.12.001

Change of Endoglucanase Activity and Rumen Microbial Community During Biodegradation of Cellulose Using Rumen Microbiota.

Treatment with rumen microorganisms improves the methane fermentation of undegradable lignocellulosic biomass; however, the role of endoglucanase in lignocellulose digestion remains unclear. This study was conducted to investigate endoglucanases contributing to cellulose degradation during treatment with rumen microorganisms, using carboxymethyl cellulose (CMC) as a substrate. The rate of CMC degradation increased for the first 24 h of treatment. Zymogram analysis revealed that endoglucanases of 52 and 53 kDa exhibited high enzyme activity for the first 12 h, whereas endoglucanases of 42, 50, and 101 kDa exhibited high enzyme activities from 12 to 24 h. This indicates that the activities of these five endoglucanases shifted and contributed to efficient CMC degradation. Metagenomic analysis revealed that the relative abundances of Selenomonas, Eudiplodinium, and Metadinium decreased after 12 h, which was positively correlated with the 52- and 53-kDa endoglucanases. Additionally, the relative abundances of Porphyromonas, Didinium, unclassified Bacteroidetes, Clostridiales family XI, Lachnospiraceae and Sphingobacteriaceae increased for the first 24 h, which was positively correlated with endoglucanases of 42, 50, and 101 kDa. This study suggests that uncharacterized and non-dominant microorganisms produce and/or contribute to activity of 40, 50, 52, 53, and 101 kDa endoglucanases, enhancing CMC degradation during treatment with rumen microorganisms.

Effects of Adding Zero Valent Iron on the Anaerobic Digestion of Cow Manure and Lignocellulose.

Previous studies showed that adding zero valent iron (ZVI) can increase the methane production and degradation rate of organic waste by improving the performance of anaerobic digester. However, our study firstly found that ZVI (37 μm, 10 g/L) inhibited the anaerobic digestion (AD) of cow manure and lignocellulose. ZVI significantly increased the methanogenic rate of cow manure in the first 6 days, but decreased the accumulative methane yield and volatile fatty acids yield by 10.3 and 12%, respectively. The effect of ZVI on AD of liquid biomass separated from cow manure was positive, but the effect on solid biomass was negative. These results indicated that ZVI enhanced the AD of easily biodegradable organics but inhibited the biodegradation of refractory organics (lignocellulose). By analyzing the varying effects of ZVI in diverse anaerobic systems, it was found that the effects were influenced by the characteristics of substrate and inoculum-substrate ratio. This study suggested that only proper ZVI addition can improve the AD process depending on the feeding materials.

Materiales biopoliméricos desarrollados a partir de micelio y residuos lignocelulósicos. Estado de la técnica actual y perspectivas de aplicación en el campo del hábitat

El micelio es un polímero producido por microorganismos, biobasado y biodegradable. Está compuesto de estructuras filamentosas (hifas), se encuentra en la naturaleza y también puede ser obtenido mediante el proceso de degradación o digestión de lignocelulosa inoculada con hongos macromicetos. La lignocelulosa es una de las sustancias más abundantes en el planeta, y se encuentra en la biomasa contenida en restos orgánicos, forestales, agrícolas y una parte importante de los residuos sólidos urbanos. En Argentina, los hongos actualmente se producen en su mayoría con fines comestibles y la parte vegetativa de las fructificaciones que se comercializan, se descarta o se utiliza como abono para suelos. Se indagó en las propiedades beneficiosas del material como así también en los métodos patentados para su fabricación. El objetivo de este trabajo es encontrar nuevos nichos de investigación en el campo del hábitat mediante un estudio antecedentes de investigaciones y producción de micelio para diversas aplicaciones.

A comparison of different oxidative pretreatments on polysaccharide hydrolyzability and cell wall structure for interpreting the greatly improved enzymatic digestibility of sugarcane bagasse by delignification

In order to confirm the contribution of delignification to the increase in lignocellulosic cellulose digestibility, several laboratory oxidative pretreatments under mild conditions, including alkaline-hydrogen peroxide (AP), two-step alkaline/peracetic acid (APAA) and sodium chlorite (SC) pretreatments were employed to achieve selective delignification of sugarcane bagasse and retained most of the hemicelluloses (xylan) in the pretreated solids. Four commercial cellulase cocktails were used to test the enzymatic hydrolyzability of pretreated substrates. Results revealed that delignification indeed could greatly improve the final (120 h) cellulose hydrolysis with relatively high final (120 h) glucan conversion (> 90%) by different cellulase cocktails even if the substrates still had a high hemicelluloses content. However, the xylan conversion seemed to be more greatly dependent on the pretreatments and cellulase cocktails used. AP and APAA pretreatments resulted in the disappearance of middle lamella and liberation of cellulose fibers with significant etching, deformation and fracture of cell wall structure. SC pretreatment greatly modified the sugar bagasse surface morphology to make the surface much coarser. The cell wall also underwent serious fracture and deformation with some middle lamella disappearing. However, no significant alteration on the structure of pure cellulose was observed by SC oxidative pretreatment of filter paper. Oxidative pretreatment might also modify lignin structure and surface properties thus greatly reducing the non-specific adsorption of enzymes. The obtained results strongly support the conclusion that delignification under mild pretreatment condition can be very helpful to improve the enzymatic hydrolysis of lignocellulosic cellulose by commercial cellulase cocktails even if the substrates has a high hemicelluloses content.

Fermentation of fibre rich ingredients exposed in vitro to the faecal inoculums of swine and turkeys.

This study was focused on in vitro fermentation and in vitro dry matter (DM) digestibility of different fibre rich ingredients that can be used in diets of pigs and turkeys. In vitro DM digestibility was determined by Daisy system via using faecal or excreta fluid of swine/turkeys as a source of inoculum. The ingredients used as substrates were commercial swine or turkey diet, dried beet pulp, wheat bran, hay, straw and two types of lignocelluloses (A and B). Marked differences between the ingredients were found and the values were: dried beet pulp (80%), swine/turkey diet (75%), wheat bran (60%), hay (40%) and straw (10%–20%). Of special interest are the data on the two lignocellulose products, the in vitro DM digestibility of product A was in the range of 20% (in turkeys) up to 30% (in pigs), whereas the product B had values of <5%. Moreover, the inoculums were incubated with the same substrates for 24h using gas measuring technique. Consecutively, commercial swine or turkey diet, dried beet pulp, wheat bran and hay produced high amounts of gas and volatile fatty acids. Lignocellulose A and straw provided lower and equal amounts of gases and fatty acids. However, lignocellulose B showed very little fermentation compared to the product A. In conclusions, faecal or excreta can be used as a source of microbial activity to determine the in vitro DM digestibility or fermentation of feeds. Comparing lignocellulose products with traditional fibre sources, the DM digestibility of lignocellulose A was greater than straw but its fermentation rate seems to be equal to straw. Thus, lignocellulose A can be used as a new source of fibre in diets of monogastric animals to optimize the gut health and improving the faeces or excreta quality.

Phylogenomic analysis of 589 metagenome-assembled genomes encompassing all major prokaryotic lineages from the gut of higher termites.

“Higher” termites have been able to colonize all tropical and subtropical regions because of their ability to digest lignocellulose with the aid of their prokaryotic gut microbiota. Over the last decade, numerous studies based on 16S rRNA gene amplicon libraries have largely described both the taxonomy and structure of the prokaryotic communities associated with termite guts. Host diet and microenvironmental conditions have emerged as the main factors structuring the microbial assemblages in the different gut compartments. Additionally, these molecular inventories have revealed the existence of termite-specific clusters that indicate coevolutionary processes in numerous prokaryotic lineages. However, for lack of representative isolates, the functional role of most lineages remains unclear. We reconstructed 589 metagenome-assembled genomes (MAGs) from the different gut compartments of eight higher termite species that encompass 17 prokaryotic phyla. By iteratively building genome trees for each clade, we significantly improved the initial automated assignment, frequently up to the genus level. We recovered MAGs from most of the termite-specific clusters in the radiation of, for example, Planctomycetes, Fibrobacteres, Bacteroidetes, Euryarchaeota, Bathyarchaeota, Spirochaetes, Saccharibacteria, and Firmicutes, which to date contained only few or no representative genomes. Moreover, the MAGs included abundant members of the termite gut microbiota. This dataset represents the largest genomic resource for arthropod-associated microorganisms available to date and contributes substantially to populating the tree of life. More importantly, it provides a backbone for studying the metabolic potential of the termite gut microbiota, including the key members involved in carbon and nitrogen biogeochemical cycles, and important clues that may help cultivating representatives of these understudied clades.

Leachate recirculation effects on solid‐state anaerobic digestion of Pennisetum hybrid and microbial community analysis

AbstractBACKGROUNDA leach‐bed reactor (LBR) with leachate recirculation is a suitable technology for lignocellulosic biomass anaerobic digestion. In this study, the effect of percolate reflux strategies (continuous recirculation and intermittent recirculation) on methane production from Pennisetum hybrid, a type of energy crop, was investigated using a two‐layered LBR.RESULTSCompared to a solid‐state anaerobic digestion batch test, LBRs with percolate recirculation provide a stable process with a short lag phase by avoiding inhibition of volatile fatty acid accumulation and inoculation effect. The results also indicated that continuous reflux led to a lower accumulative methane yield (56.20 L kg−1 VS) compared to intermittent reflux (78.50 L kg−1 VS), resulting from washing effect and poorer distribution on the lower layer. According to microbial analysis, Bacteroidetes, Firmicutes, Proteobacteria and Synergistetes were the most predominant bacterial phyla in each LBR test sample and aceticlastic methanogen (at least &gt;55%) plays a predominant role for methane production in all samples.CONCLUSIONSThe results indicate that leachate recirculation could provide stable conditions for methane yield; however, two‐layer reactor designs which cannot guarantee the desired distribution in the lower layer result in a low methane yield. Suitable design of LBRs to maintain a well‐distributed reflux leachate should be further investigated. © 2019 Society of Chemical Industry

Extraction and characterization of endogenous cellulases in giant African land snail, Achatina fulica for lignocellulose digestion

Extraction and characterization of endogenous cellulases in giant African land snail, Achatina fulica for lignocellulose digestion

Combined simultaneous enzymatic saccharification and comminution (SESC) and anaerobic digestion for sustainable biomethane generation from wood lignocellulose and the biochemical characterization of residual sludge solid

Simultaneous enzymatic saccharification and comminution (SESC) was used for large-scale anaerobic digestion of wood lignocellulose to generate methane and unmodified lignin. During SESC, 10% aqueous mixture of powdered debarked wood from various species was subjected to bead milling with hydrolytic enzymes to generate particles below 1 μm. This slurry was directly used as a cosubstrate for anaerobic digestion in a 500 L stirred-tank reactor. Temperature and hydraulic retention time (HRT) were maintained at 50 °C and 30 days, respectively. At stable operation periods, an average yield of 224 L of methane per kg of cedar was attained. Comparable yields were achieved with red pine, elm, oak, and cedar bark. High-throughput microbial analysis established the presence of a relevant community to support the elevated level of methane production. The stability of the unmodified lignin in anaerobic digestion was also confirmed, allowing for its recovery as an important by-product.

The evolution and genomic basis of beetle diversity

The order Coleoptera (beetles) is arguably the most speciose group of animals, but the evolutionary history of beetles, including the impacts of plant feeding (herbivory) on beetle diversification, remain poorly understood. We inferred the phylogeny of beetles using 4,818 genes for 146 species, estimated timing and rates of beetle diversification using 89 genes for 521 species representing all major lineages and traced the evolution of beetle genes enabling symbiont-independent digestion of lignocellulose using 154 genomes or transcriptomes. Phylogenomic analyses of these uniquely comprehensive datasets resolved previously controversial beetle relationships, dated the origin of Coleoptera to the Carboniferous, and supported the codiversification of beetles and angiosperms. Moreover, plant cell wall-degrading enzymes (PCWDEs) obtained from bacteria and fungi via horizontal gene transfers may have been key to the Mesozoic diversification of herbivorous beetles-remarkably, both major independent origins of specialized herbivory in beetles coincide with the first appearances of an arsenal of PCWDEs encoded in their genomes. Furthermore, corresponding (Jurassic) diversification rate increases suggest that these novel genes triggered adaptive radiations that resulted in nearly half of all living beetle species. We propose that PCWDEs enabled efficient digestion of plant tissues, including lignocellulose in cell walls, facilitating the evolution of uniquely specialized plant-feeding habits, such as leaf mining and stem and wood boring. Beetle diversity thus appears to have resulted from multiple factors, including low extinction rates over a long evolutionary history, codiversification with angiosperms, and adaptive radiations of specialized herbivorous beetles following convergent horizontal transfers of microbial genes encoding PCWDEs.

Species-wide Metabolic Interaction Network for Understanding Natural Lignocellulose Digestion in Termite Gut Microbiota

The structural complexity of lignocellulosic biomass hinders the extraction of cellulose, and it has remained a challenge for decades in the biofuel production process. However, wood-feeding organisms like termite have developed an efficient natural lignocellulolytic system with the help of specialized gut microbial symbionts. Despite having an enormous amount of high-throughput metagenomic data, specific contributions of each individual microbe to achieve this lignocellulolytic functionality remains unclear. The metabolic cross-communication and interdependence that drives the community structure inside the gut microbiota are yet to be explored. We have contrived a species-wide metabolic interaction network of the termite gut-microbiome to have a system-level understanding of metabolic communication. Metagenomic data of Nasutitermes corniger have been analyzed to identify microbial communities in different gut segments. A comprehensive metabolic cross-feeding network of 205 microbes and 265 metabolites was developed using published experimental data. Reconstruction of inter-species influence network elucidated the role of 37 influential microbes to maintain a stable and functional microbiota. Furthermore, in order to understand the natural lignocellulose digestion inside N. corniger gut, the metabolic functionality of each influencer was assessed, which further elucidated 15 crucial hemicellulolytic microbes and their corresponding enzyme machinery.