Parallel metatranscriptome analyses of host and symbiont gene expression in the gut of the termite Reticulitermes flavipes

Inheritance or Recruitment? The Assembly Mechanisms and Functional Dynamics of Microbial Communities in the Life Cycle of a Wood-Feeding Beetle

Microbial partners enhance the metabolic capabilities of insects, enabling their adaptation to diverse ecological niches. Xylophagous insects have larvae that can digest lignocellulose and cope with plant secondary metabolites (PSMs). However, there is little information in terms of microbiome sources, dynamics and species contributions. This limits our understanding of the interaction between xylophagous insects and the microbiome. Monochamus saltuarius (Cerambycidae) is a significant borer of conifers. We used combined qPCR, host genomic and microbiome metagenomic datasets, as well as in vitro validation experiments to study the dynamics of the associated microbiome and its interactions with M. saltuarius. We evaluated microbial metabolic/biosynthetic contributions and validated their related functions. Our findings revealed that insect growth and development altered the quantity and community composition of associated bacteria and fungi. The egg microbiome was particularly susceptible to alteration due to oviposition pits. Bacterial transmission largely persisted between developmental stages, while fungal re-acquisition primarily originated from the external environment. By reconstructing community pathway maps, we identified the cooperative interactions between the insect and its gut microbiome. As larvae transitioned from phloem to xylem feeding, the functional role of the gut microbiome in various pathways was weakened. Remarkably, high-contribution bacterial species largely overlapped across different functional roles, and these species also showed considerable overlap between phloem and xylem feeding periods. Overall, our study highlights the unique interaction between xylophagous insects and their microbiome, which enhances their ability in lignocellulose digestion, PSMs degradation and the acquisition of essential amino acids, as well as vitamins.

Involvement of a catalase gene in lignin catalysis and immune defense against pathogenic fungus in Coptotermes formosanus: a potential new target for termite control

BACKGROUND

Detoxifying enzymes are likely involved in lignin feeding and immune defense mechanisms within termites, rendering them potential targets for biological control. However, investigations into the dual functionality of termite detoxification enzymes in vivo have not been documented.

RESULTS

In this study, the complete cDNA of the catalase gene (Cfcat) derived from Coptotermes formosanus Shiraki was amplified. CFCAT comprises an open reading frame spanning 1527 bp, encoding a 508-amino acid sequence. The highest expression was observed in the epidermal tissues (including the fat body and hemolymph) followed by the foregut/salivary gland. Furthermore, we confirmed the catalase activity of the recombinant Cfcat protein. Using RNA interference (RNAi) technology, the importance of Cfcat in the lignin-feeding of C. formosanus was demonstrated, and the role of Cfcat in innate immunity was investigated. Survival assays showed that Cfcat RNAi significantly increased the susceptibility of C. formosanus to Metarhizium anisopliae. Irrespective of the infection status, Cfcat inhibition had a significant impact on multiple factors of humoral and intestinal immunity in C. formosanus. Notably, Cfcat RNAi exhibited a more pronounced immunosuppressive effect on humoral immunity than on intestinal immunity.

CONCLUSION

Cfcat plays an important role in the regulation of innate immunity and lignin feeding in C. formosanus. Cfcat RNAi can weaken the immune response of termites against M. anisopliae, which may aid the biocontrol efficiency of M. anisopliae against C. formosanus. This study provides a theoretical basis and technical reference for the development of a novel biocontrol strategy targeting detoxifying enzymes of termites. © 2024 Society of Chemical Industry.

Seasonal impacts on gut microbial composition of the Eastern subterranean termite (Blattodea: Rhinotermitidae)

Termite hindguts are inhabited by symbionts that help with numerous processes, but changes in the gut microbiome due to season can potentially impact the physiology of termites. This study investigated the impact of seasonal changes on the composition of bacteria and protozoa in the termite gut. Termites were obtained monthly from May to October 2020 at a location in the central United States that typically experiences seasonal air temperatures ranging from < 0 to > 30 °C. The guts of 10 termites per biological replication were dissected and frozen within 1 day after collections. DNA was extracted from the frozen gut tissues and used for termite 16S rRNA mitochondrial gene analysis and bacterial 16S rRNA gene sequence surveys. Phylogenetic analysis of termite 16S rRNA gene sequences verified that the same colony was sampled across all time points. On processing bacterial 16S sequences, we observed alpha (observed features, Pielou's evenness, and Shannon diversity) and beta diversity (unweighted Unifrac, Bray-Curtis, and Jaccard) metrics to vary significantly across months. Based on the analysis of the composition of microbiomes with bias correction (ANCOM-BC) at the genus level, we found several significant bacterial taxa over collection months. In addition, Spearman correlation analysis demonstrated that 41 bacterial taxa were significantly correlated (positively and negatively) with average soil temperature. These results from a single termite colony suggest termite microbial communities go through seasonal changes in relative abundance related to temperature, although other seasonal effects cannot be excluded. Further investigations are required to conclusively define the consistency of microbial variation among different colonies with season.

Molecular unraveling of polysaccharide digestion in wood-feeding termites: A solid-state NMR perspective

Termites are among the most efficient organisms utilizing polysaccharides from wood and play a significant role in global carbon recycling, especially within tropical and subtropical ecosystems. Yet, the molecular details in polysaccharide degradation by termites remain largely unexplored. In this work, we have elucidated the shared and distinct molecular details in polysaccharides digestion by the higher termite Nasutitermes on poplar and the lower termite Cryptotermes on pine using high resolution solid-state nuclear magnetic resonance spectroscopy. For the first time, structural polymers are partitioned into the minor mobile and dominant rigid phases for individual examination. The mobile polysaccharides receive less structural impacts and exhibit greater digestibility compared to the rigid counterparts. While both termites effectively degrade cellulose, Nasutitermes significantly outperforms Cryptotermes in hemicellulose breakdown. In the rigid phase, cellulose is comprehensively degraded into a fragmented and more dynamically consistent structure; As Nasutitermes breaks down hemicellulose in a similar manner to cellulose, Cryptotermes selectively digests hemicellulose at its interfaces with cellulose. Additionally, crystalline cellulose undergoes selective degradation, and the digestion of amorphous cellulose might involve sugar chain detachment within microfibrils. Overall, our findings offer significant advancements and fresh perspectives on the polysaccharide digestion strategies of different termite lineages.

Termite Microbial Symbiosis as a Model for Innovative Design of Lignocellulosic Future Biorefinery: Current Paradigms and Future Perspectives

The hunt for renewable and alternative fuels has driven research towards the biological conversion of lignocellulosic biomass (LCB) into biofuels, including bioethanol and biohydrogen. Among the natural biomass utilization systems (NBUS), termites represent a unique and easy-to-access model system to study host–microbe interactions towards lignocellulose bioconversion/valorization. Termites have gained significant interest due to their highly efficient lignocellulolytic systems. The wood-feeding termites apply a unique and stepwise process for the hydrolysis of lignin, hemicellulose, and cellulose via biocatalytic processes; therefore, mimicking their digestive metabolism and physiochemical gut environments might lay the foundation for an innovative design of nature-inspired biotechnology. This review highlights the gut system of termites, particularly the wood-feeding species, as a unique model for future biorefinery. The gut system of termites is a treasure-trove for prospecting novel microbial species, including protists, bacteria, and fungi, having higher biocatalytic efficiencies and biotechnological potentials. The significance of potential bacteria and fungi for harnessing the enzymes appropriate for lignocellulosic biorefinery is also discussed. Termite digestomes are rich sources of lignocellulases and related enzymes that could be utilized in various industrial processes and biomass-related applications. Consideration of the host and symbiont as a single functioning unit will be one of the most crucial strategies to expedite developments in termite-modeled biotechnology in the future.

Wood feeding and social living: Draft genome of the subterranean termite Reticulitermes lucifugus (Blattodea; Termitoidae)

Termites (Insecta, Blattodea, Termitoidae) are a widespread and diverse group of eusocial insects known for their ability to digest wood matter. Herein, we report the draft genome of the subterranean termite Reticulitermes lucifugus, an economically important species and among the most studied taxa with respect to eusocial organization and mating system. The final assembly (~813 Mb) covered up to 88% of the estimated genome size and, in agreement with the Asexual Queen Succession Mating System, it was found completely homozygous. We predicted 16,349 highly supported gene models and 42% of repetitive DNA content. Transposable elements of R. lucifugus show similar evolutionary dynamics compared to that of other termites, with two main peaks of activity localized at 25% and 8% of Kimura divergence driven by DNA, LINE and SINE elements. Gene family turnover analyses identified multiple instances of gene duplication associated with R. lucifugus diversification, with significant lineage-specific gene family expansions related to development, perception and nutrient metabolism pathways. Finally, we analysed P450 and odourant receptor gene repertoires in detail, highlighting the large diversity and dynamical evolutionary history of these proteins in the R. lucifugus genome. This newly assembled genome will provide a valuable resource for further understanding the molecular basis of termites biology as well as for pest control.

A holobiont approach towards polysaccharide degradation by the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis

BACKGROUND

Termites are among the most successful insects on Earth and can feed on a broad range of organic matter at various stages of decomposition. The termite gut system is often referred to as a micro-reactor and is a complex structure consisting of several components. It includes the host, its gut microbiome and fungal gardens, in the case of fungi-growing higher termites. The digestive tract of soil-feeding higher termites is characterised by radial and axial gradients of physicochemical parameters (e.g. pH, O₂ and H₂ partial pressure), and also differs in the density and structure of residing microbial communities. Although soil-feeding termites account for 60% of the known termite species, their biomass degradation strategies are far less known compared to their wood-feeding counterparts.

RESULTS

In this work, we applied an integrative multi-omics approach for the first time at the holobiont level to study the highly compartmentalised gut system of the soil-feeding higher termite Labiotermes labralis. We relied on 16S rRNA gene community profiling, metagenomics and (meta)transcriptomics to uncover the distribution of functional roles, in particular those related to carbohydrate hydrolysis, across different gut compartments and among the members of the bacterial community and the host itself. We showed that the Labiotermes gut was dominated by members of the Firmicutes phylum, whose abundance gradually decreased towards the posterior segments of the hindgut, in favour of Bacteroidetes, Proteobacteria and Verrucomicrobia. Contrary to expectations, we observed that L. labralis gut microbes expressed a high diversity of carbohydrate active enzymes involved in cellulose and hemicelluloses degradation, making the soil-feeding termite gut a unique reservoir of lignocellulolytic enzymes with considerable biotechnological potential. We also evidenced that the host cellulases have different phylogenetic origins and structures, which is possibly translated into their different specificities towards cellulose. From an ecological perspective, we could speculate that the capacity to feed on distinct polymorphs of cellulose retained in soil might have enabled this termite species to widely colonise the different habitats of the Amazon basin.

CONCLUSIONS

Our study provides interesting insights into the distribution of the hydrolytic potential of the highly compartmentalised higher termite gut. The large number of expressed enzymes targeting the different lignocellulose components make the Labiotermes worker gut a relevant lignocellulose-valorising model to mimic by biomass conversion industries.

Prophenoloxidase of Odontotermes formosanus (Shiraki) (Blattodea: Termitidae) Is a Key Gene in Melanization and Has a Defensive Role during Bacterial Infection

Melanization mediated by the prophenoloxidase (PPO)-activating system is an important innate immunity to fight pathogens in insects. In this study, the in vitro time-dependent increase in the intensity of melanization and phenoloxidase (PO) activity from the hemolymph of Odontotermes formosanus (Shiraki) challenged by pathogenic bacteria was detected. PPO is one of the key genes in melanization pathway, whereas the molecular characteristics and functions of O. formosanus PPO are unclear. The OfPPO gene was cloned and characterized. The open reading frame of OfPPO is 2085 bp in length and encodes a 79.497 kDa protein with 694 amino acids. A BLASTx search and phylogenetic analyses revealed that OfPPO shares a high degree of homology to the Blattodea PPOs. Moreover, real-time fluorescent quantitative PCR analysis showed that OfPPO is ubiquitously expressed in all castes and tissues examined, with the highest expression in workers and variable expression patterns in tissues of different termite castes. Furthermore, the expression of OfPPO was significantly induced in O. formosanus infected by pathogenic bacteria. Intriguingly, in combination with silencing of OfPPO expression, pathogenic bacteria challenge caused greatly increased mortality of O. formosanus. These results suggest that OfPPO plays a role in defense against bacteria and highlight the novel termite control strategy combining pathogenic bacteria application with termite PPO silencing.

CAZyme from gut microbiome for efficient lignocellulose degradation and biofuel production

Over-exploitation and energy security concerns of the diminishing fossil fuels is a challenge to the present global economy. Further, the negative impact of greenhouse gases released using conventional fuels has led to the need for searching for alternative biofuel sources with biomass in the form of lignocellulose coming up as among the potent candidates. The entrapped carbon source of the lignocellulose has multiple applications other than biofuel generation under the biorefinery approach. However, the major bottleneck in using lignocellulose for biofuel production is its recalcitrant nature. Carbohydrate Active Enzymes (CAZymes) are enzymes that are employed for the disintegration and consumption of lignocellulose biomass as the carbon source for the production of biofuels and bio-derivatives. However, the cost of enzyme production and their stability and catalytic efficiency under stressed conditions is a concern that hinders large-scale biofuel production and utilization. Search for novel CAZymes with superior activity and stability under industrial condition has become a major research focus in this area considering the fact that the most conventional CAZymes has low commercial viability. The gut of plant-eating herbivores and other organisms is a potential source of CAZyme with high efficiency. The review explores the potential of the gut microbiome of various organisms in the production of an efficient CAZyme system and the challenges in using the biofuels produced through this approach as an alternative to conventional biofuels.

Insecticidal Serralysin of Serratia marcescens Is Detoxified in M3 Midgut Region of Riptortus pedestris

Riptortus pedestris insect indiscriminately acquires not only the symbiotic bacterium Burkholderia insecticola, but also entomopathogens that are abundant in the soil via feeding. However, it is unclear how the host insect survives oral infections of entomopathogens. A previous study suggested that serralysin, a potent virulence factor produced by Serratia marcescens, suppresses cellular immunity by degrading adhesion molecules, thereby contributing to bacterial pathogenesis. Here, we observed that S. marcescens orally administered to R. pedestris stably colonized the insect midgut, while not exhibiting insecticidal activity. Additionally, oral infection with S. marcescens did not affect the host growth or fitness. When co-incubated with the midgut lysates of R. pedestris, serralysin was remarkably degraded. The detoxification activity against serralysin was enhanced in the midgut extract of gut symbiont-colonizing insects. The mRNA expression levels of serralysin genes were negligible in M3-colonizing S. marcescens. M3-colonizing S. marcescens did not produce serralysin toxin. Immunoblot analyses revealed that serralysin was not detected in the M3 midgut region. The findings of our study suggest that orally infected S. marcescens lose entomopathogenicity through host-derived degrading factors and suppression of serralysin.

The functional evolution of termite gut microbiota

BACKGROUND

Termites primarily feed on lignocellulose or soil in association with specific gut microbes. The functioning of the termite gut microbiota is partly understood in a handful of wood-feeding pest species but remains largely unknown in other taxa. We intend to fill this gap and provide a global understanding of the functional evolution of termite gut microbiota.

RESULTS

We sequenced the gut metagenomes of 145 samples representative of the termite diversity. We show that the prokaryotic fraction of the gut microbiota of all termites possesses similar genes for carbohydrate and nitrogen metabolisms, in proportions varying with termite phylogenetic position and diet. The presence of a conserved set of gut prokaryotic genes implies that essential nutritional functions were present in the ancestor of modern termites. Furthermore, the abundance of these genes largely correlated with the host phylogeny. Finally, we found that the adaptation to a diet of soil by some termite lineages was accompanied by a change in the stoichiometry of genes involved in important nutritional functions rather than by the acquisition of new genes and pathways.

CONCLUSIONS

Our results reveal that the composition and function of termite gut prokaryotic communities have been remarkably conserved since termites first appeared ~ 150 million years ago. Therefore, the "world's smallest bioreactor" has been operating as a multipartite symbiosis composed of termites, archaea, bacteria, and cellulolytic flagellates since its inception. Video Abstract.

Diet Fermentation Leads to Microbial Adaptation in Black Soldier Fly (Hermetia illucens; Linnaeus, 1758) Larvae Reared on Palm Oil Side Streams

Insects offer a promising alternative source of protein to mitigate the environmental consequences of conventional livestock farming. Larvae of the black soldier fly (Hermetia illucens; Linnaeus, 1758) efficiently convert a variety of organic side streams and residues into valuable proteins, lipids, and chitin. Here, we evaluated the suitability of two palm oil industry side streams—empty fruit bunches (EFB) and palm kernel meal (PKM)—as larval feed, and their impact on the larval gut microbiome. Among 69 fungal species we screened, Marasmius palmivorus, Irpex consors, and Bjerkandera adusta achieved the fastest growth and lignin degradation, so these fungi were used for the pretreatment of 7:3 mixtures of EFB and PKM. Larvae reared on the mixture pretreated with B. adusta (BAD) developed significantly more quickly and reached a higher final weight than those reared on the other pretreatments or the non-fermented reference (NFR). Amplicon sequencing of the BAD and NFR groups revealed major differences in the larval gut microbiome. The NFR group was dominated by facultatively anaerobic Enterobacteriaceae (typical of H. illucens larvae) whereas the BAD group favored obligately anaerobic, cellulolytic bacteria (Ruminococcaceae and Lachnospiraceae). We hypothesize that fungal lignin degradation led to an accumulation of mycelia and subsequent cellulolytic breakdown of fiber residues, thus improving substrate digestibility.

Identification of a New Endo-β-1,4-xylanase Prospected from the Microbiota of the Termite Heterotermes tenuis

Xylanases are hemicellulases that break down xylan to soluble pentoses. They are used for industrial purposes, such as paper whitening, beverage clarification, and biofuel production. The second-generation bioethanol production is hindered by the enzymatic hydrolysis step of the lignocellulosic biomass, due to the complex arrangement established among its constituents. Xylanases can potentially increase the production yield by improving the action of the cellulolytic enzyme complex. We prospected endo-β-1,4-xylanases from meta-transcriptomes of the termite Heterotermes tenuis. In silico structural characterization and functional analysis of an endo-β-1,4-xylanase from a symbiotic protist of H. tenuis indicate two active sites and a substrate-binding groove needed for the catalytic activity. No N-glycosylation sites were found. This endo-β-1,4-xylanase was recombinantly expressed in Pichia pastoris and Escherichia coli cells, presenting a molecular mass of approximately 20 kDa. Enzymatic activity assay using recombinant endo-β-1,4-xylanase was also performed on 1% xylan agar stained with Congo red at 30 °C and 40 °C. The enzyme expressed in both systems was able to hydrolyze the substrate xylan, becoming a promising candidate for further analysis aiming to determine its potential for application in industrial xylan degradation processes.

How Do Shipworms Eat Wood? Screening Shipworm Gill Symbiont Genomes for Lignin-Modifying Enzymes

Shipworms are ecologically and economically important mollusks that feed on woody plant material (lignocellulosic biomass) in marine environments. Digestion occurs in a specialized cecum, reported to be virtually sterile and lacking resident gut microbiota. Wood-degrading CAZymes are produced both endogenously and by gill endosymbiotic bacteria, with extracellular enzymes from the latter being transported to the gut. Previous research has predominantly focused on how these animals process the cellulose component of woody plant material, neglecting the breakdown of lignin – a tough, aromatic polymer which blocks access to the holocellulose components of wood. Enzymatic or non-enzymatic modification and depolymerization of lignin has been shown to be required in other wood-degrading biological systems as a precursor to cellulose deconstruction. We investigated the genomes of five shipworm gill bacterial symbionts obtained from the Joint Genome Institute Integrated Microbial Genomes and Microbiomes Expert Review for the production of lignin-modifying enzymes, or ligninases. The genomes were searched for putative ligninases using the Joint Genome Institute’s Function Profile tool and blastp analyses. The resulting proteins were then modeled using SWISS-MODEL. Although each bacterial genome possessed at least four predicted ligninases, the percent identities and protein models were of low quality and were unreliable. Prior research demonstrates limited endogenous ability of shipworms to modify lignin at the chemical/molecular level. Similarly, our results reveal that shipworm bacterial gill-symbiont enzymes are unlikely to play a role in lignin modification during lignocellulose digestion in the shipworm gut. This suggests that our understanding of how these keystone organisms digest and process lignocellulose is incomplete, and further research into non-enzymatic and/or other unknown mechanisms for lignin modification is required.

Comparative analyses of transcriptional responses of Dectes texanus LeConte (Coleoptera: Cerambycidae) larvae fed on three different host plants and artificial diet

Dectes texanus is an important coleopteran pest of soybeans and cultivated sunflowers in the Midwestern United States that causes yield losses by girdling stems of their host plants. Although sunflower and giant ragweed are primary hosts of D. texanus, they began colonizing soybeans approximately 50 years ago and no reliable management method has been established to prevent or reduce losses by this pest. To identify genes putatively involved when feeding soybean, we compared gene expression of D. texanus third-instar larvae fed soybean to those fed sunflower, giant ragweed, or artificial diet. Dectes texanus larvae differentially expressed 514 unigenes when fed on soybean compared to those fed the other diet treatments. Enrichment analyses of gene ontology terms from up-regulated unigenes in soybean-fed larvae compared to those fed both primary hosts highlighted unigenes involved in oxidoreductase and polygalacturonase activities. Cytochrome P450s, carboxylesterases, major facilitator superfamily transporters, lipocalins, apolipoproteins, glycoside hydrolases 1 and 28, and lytic monooxygenases were among the most commonly up-regulated unigenes in soybean-fed larvae compared to those fed their primary hosts. These results suggest that D. texanus larvae differentially expressed unigenes involved in biotransformation of allelochemicals, digestion of plant cell walls and transport of small solutes and lipids when feeding in soybean.

Collaborative Response of the Host and Symbiotic Lignocellulytic System to Non-Lethal Toxic Stress in Coptotermes formosanus Skiraki

Simple Summary

Coptotermes formosanus Shiraki is a wood feeding lower termite and is widely distributed in many areas. The dynamic adjustment of the C. formosanus digestive system to unfavorable survival environments was investigated via non-lethal toxic feeding. The toxic stress did not change the dominant role of microbial lignocellulases in cellulose degradation of C. formosanus. The core symbiotic community was stable in abundance during the tolerance to the toxic treatment. However, a large number of low abundance taxa were significantly enriched by the low toxic feeding. These rare bacterial lineages likely contribute to toxic stress tolerance of termite. Above all, these findings add important new knowledge to our understanding of environmental adaptation of the lignocellulose hydrolysis system in termites.

Abstract

Disturbing the lignocellulose digestive system of termites is considered to be a promising approach for termite control. The research on the tolerance mechanism of the termite lignocellulose digestive system to harmful environment conditions is limited. In this study, we keep Coptotermes formosanus Skiraki under a non-lethal toxic condition by feeding the termites with filter paper containing the kojic acid (a low toxic insecticide). The effects of low toxic stress on the activities and gene expressions of host/symbiotic originated lignocellulases, and on the symbiotic microbial community structure of C. formosanus were explored. Our result showed that the low toxic stress would lead to the synchronous decrease of cellulase and hemicellulase activities, and supplementary increase of corresponding gene expressions. The symbiotic community maintained its role as the main force in the lignocellulolytic system of C. formosanus. Meanwhile, a large number of rare taxa were significantly enriched by kojic acid treatment. These numerically inconspicuous bacterial populations might be responsible for the functions similar to phenoloxidase or insecticide detoxification and enable C. formosanus to tolerate the harmful environment. Overall, our data suggested that the digestive adaptation of C. formosanus to physiotoxic feeding is closely related to the triple collaboration of termites–flagellates–bacteria.

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

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.

Expression profiles of neotropical termites reveal microbiota-associated, caste-biased genes and biotechnological targets

Termites are well recognized by their complex development trajectories, involving dynamic differentiation process between non-reproductive castes, workers and soldiers. These insects are associated with endosymbiotic microorganisms, which help in lignocellulose digestion and nitrogen metabolism. Aiming to identify genes harbouring biotechnological potential, we analyzed workers and soldiers RNA-Seq data of three neotropical termites: Heterotermes tenuis (Isoptera: Rhinotermitidae), Velocitermes heteropterus (Isoptera: Termitidae) and Cornitermes cumulans (Isoptera: Termitidae). We observed differences in the microbiota associated with each termite family, and found protists' genes in both Termitidae species. We found an opposite pattern of caste-biased gene expression between H. tenuis and the termitids studied. Moreover, the two termitids are considerably different concerning the number of differentially expressed genes (DEGs). Functional annotation indicated considerable differences in caste-biased gene content between V. heteropterus and C. cumulans, even though they share similar diet and biological niche. Among the most DEGs, we highlighted those involved in caste differentiation and cellulose digestion, which are attractive targets for studying more efficient technologies for termite control, biomass digestion and other biotechnological applications.

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.

Functional and structural characterization of a novel GH3 β-glucosidase from the gut metagenome of the Brazilian Cerrado termite Syntermes wheeleri

In this study, a GH3 family β-glucosidase (Bgl7226) from metagenomic sequences of the Syntermes wheeleri gut, a Brazilian Cerrado termite, was expressed, purified and characterized. The enzyme showed two optimum pHs (pH 7 and pH 10), and a maximum optimum temperature of about 40 °C using 4-Nitrophenyl β-D-glucopyranoside (pNPG) as substrate. Bgl7226 showed higher enzymatic activity at basic pH, but higher affinity (K_m) at neutral pH. However, at neutral pH the Bgl7226 enzyme showed higher catalytic efficiency (k_cat/K_m) for pNPG substrate. Predictive analysis about the enzyme structure-function relationship by sequence alignment suggested the presence of multi-domains and conserved catalytic sites. Circular dichroism results showed that the secondary structure composition of the enzyme is pH-dependent. Small conformational changes occurred close to the optimum temperature of 40 ^o C, and seem important for the highest activity of Bgl7226 observed at pH 7 and 10. In addition, the small transition in the unfolding curves close to 40 ^o C is typical of intermediates associated with proteins structured in several domains. Bgl7226 has significant β-glucosidase activity which could be attractive for biotechnological applications, such as plant roots detoxification; specifically, our group is interested in cassava roots (Manihot esculenta) detoxification.

Isolation, Expression Profiling, and Regulation via Host Allelochemicals of 16 Glutathione S-Transferases in the Chinese White Pine Beetle, Dendroctonus armandi

The Chinese white pine beetle (Dendroctonus armandi) is undoubtedly one of the most important pests causing ecological damage in the Qinling Mountains. When bark beetles invade conifers, they must overcome host tree defenses, including primary resistance and induced resistance responses. Moreover, this induced resistance occurs following herbivory by bark beetles. Bark beetles have a corresponding defense mechanism for degrading toxic compounds, and glutathione S-transferases (GSTs) can catalyze the binding of endogenous substances that reduce glutathione (GSH) to various harmful electrophilic substrates, increasing their solubility and facilitating their excretion from cells. In this experiment, we successfully obtained sixteen full-length sequences of D. armandi, which belonged to four GST categories (delta, epsilon, sigma, and theta). The transcript levels of sixteen GSTs in D. armandi were compared at four developmental stages (larvae, pupae, teneral adults, and adults), three different tissues (antennae, gut, and reproductive organs), and under various levels of terpenoid stimuli during feeding on phloem tissue to evaluate the various relevant modes of action. This study aids in the understanding of the interaction between monoterpenes and beetles, and beetles’ detoxification through GSTs.

Division of functional roles for termite gut protists revealed by single-cell transcriptomes

The microbiome in the hindgut of wood-feeding termites comprises various species of bacteria, archaea, and protists. This gut community is indispensable for the termite, which thrives solely on recalcitrant and nitrogen-poor wood. However, the difficulty in culturing these microorganisms has hindered our understanding of the function of each species in the gut. Although protists predominate in the termite gut microbiome and play a major role in wood digestion, very few culture-independent studies have explored the contribution of each species to digestion. Here, we report single-cell transcriptomes of four protists species comprising the protist population in worldwide pest Coptotermes formosanus. Comparative transcriptomic analysis revealed that the expression patterns of the genes involved in wood digestion were different among species, reinforcing their division of roles in wood degradation. Transcriptomes, together with enzyme assays, also suggested that one of the protists, Cononympha leidyi, actively degrades chitin and assimilates it into amino acids. We propose that C. leidyi contributes to nitrogen recycling and inhibiting infection from entomopathogenic fungi through chitin degradation. Two of the genes for chitin degradation were further revealed to be acquired via lateral gene transfer (LGT) implying the importance of LGT in the evolution of symbiosis. Our single-cell-based approach successfully characterized the function of each protist in termite hindgut and explained why the gut community includes multiple species.

Challenges and physiological implications of wood feeding in termites

Termites are fascinating insects for a number of reasons, one of which being their specialization on diets of wood lignocellulose. The goal of this review is to consider stress-inducing characteristics of wood and apparent molecular-physiological adaptations in termite guts to overcome these stressors. Defensive factors present in wood include extractive secondary plant metabolites, lignin and related phenolics, crystalline cellulose, and low nitrogen content. Molecular-physiological adaptations of the termite gut to deal with these factors include robust detoxification and antioxidant machinery, the production of a peritrophic matrix and a wide range of cellulases from host and symbiotic sources, and creation of niches available to nitrogen-fixing bacterial symbionts. Considering termite gut physiology and symbioses in the context of stress-response has applied implications. These outcomes can include development of efficient biomass breakdown strategies, protection of microbes during industrial processing applications, and safeguarding wooden structures from termite damage.

Enzymatic removal of inhibitory compounds from lignocellulosic hydrolysates for biomass to bioproducts applications

The physicochemical pretreatment is an important step to reduce biomass recalcitrance and facilitate further processing of plant lignocellulose into bioproducts. This process results in soluble and insoluble biomass fractions, and both may contain by-products that inhibit enzymatic biocatalysts and microbial fermentation. These fermentation inhibitory compounds (ICs) are produced during the degradation of lignin and sugars, resulting in phenolic and furanic compounds, and carboxylic acids. Therefore, detoxification steps may be required to improve lignocellulose conversion by microoganisms. Several physical and chemical methods, such as neutralization, use of activated charcoal and organic solvents, have been developed and recommended for removal of ICs. However, biological processes, especially enzyme-based, have been shown to efficiently remove ICs with the advantage of minimizing environmental issues since they are biogenic catalysts and used in low quantities. This review focuses on describing several enzymatic approaches to promote detoxification of lignocellulosic hydrolysates and improve the performance of microbial fermentation for the generation of bioproducts. Novel strategies using classical carbohydrate active enzymes (CAZymes), such as laccases (AA1) and peroxidases (AA2), as well as more advanced strategies using prooxidant, antioxidant and detoxification enzymes (dubbed as PADs), i.e. superoxide dismutases, are discussed as perspectives in the field.

Integrative omics analysis of the termite gut system adaptation to Miscanthus diet identifies lignocellulose degradation enzymes

Miscanthus sp. biomass could satisfy future biorefinery value chains. However, its use is largely untapped due to high recalcitrance. The termite and its gut microbiome are considered the most efficient lignocellulose degrading system in nature. Here, we investigate at holobiont level the dynamic adaptation of Cortaritermes sp. to imposed Miscanthus diet, with a long-term objective of overcoming lignocellulose recalcitrance. We use an integrative omics approach combined with enzymatic characterisation of carbohydrate active enzymes from termite gut Fibrobacteres and Spirochaetae. Modified gene expression profiles of gut bacteria suggest a shift towards utilisation of cellulose and arabinoxylan, two main components of Miscanthus lignocellulose. Low identity of reconstructed microbial genomes to closely related species supports the hypothesis of a strong phylogenetic relationship between host and its gut microbiome. This study provides a framework for better understanding the complex lignocellulose degradation by the higher termite gut system and paves a road towards its future bioprospecting.

Through metagenomics and metatranscriptomics analyses, Calusinska et al. investigate the adaptation of the gut microbiome of the termite Cortaritermes sp. to a diet of Miscanthus grass. This work is a starting point for the identification of lignocellulose-degradation enzymes for potential biotechnology applications.

Purification and Biochemical Characterization of Alkalophilic Cellulase from the Symbiotic Bacillus subtilis BC1 of the Leopard Moth, Zeuzera pyrina (L.) (Lepidoptera: Cossidae)

In the current study, an extracellular cellulase belonging to symbiotic Bacillus subtilis Bc1 of the leopard moth is purified and characterized. The molecular mass of enzyme was 47.8 kDa using SDS-PAGE. The purified enzyme had optimum activity in temperature and pH around 60 °C and 8, respectively. The purified cellulase was introduced as a stable enzyme in a wide variety of temperature (20-80 °C) and pH (4-10) and remained active to more than 74% at 80 °C for 1 h. Moreover, the cellulase extremely was stabled in the presence of metal ions and organic solvents and its activity was increased by acetone (20% v/v), CaCl₂ and CoCl₂ and inhibited by MnCl₂ and NiCl₂. The values of enzyme's K_m and V_max were found to be 1.243 mg/mL and 271.3 µg/mL/min, respectively. The purified cellulase hydrolyzed cellulose, avicel and carboxymethyl cellulose (CMC) and the final product of CMC hydrolysis was cellobiose using thin-layer chromatography analysis. Consequently, owing to exo/endoglucanase activity and organic solvent, temperature and pH stability of the purified cellulase belong to B. subtilis BC1, it can be properly employed for various industrial purposes.

A Natural High-Sugar Diet Has Different Effects on the Prokaryotic Community Structures of Lower and Higher Termites (Blattaria)

The lignocellulosic digestive symbiosis in termites is a dynamic survival adaptation system. While the contribution of hereditary and habitat factors to the development of the symbiotic bacterial community of termites had been confirmed, the manner in which these factors affect functional synergism among different bacterial lineages has still not been fully elucidated. Therefore, the 16S rRNA gene libraries of Odontotermes formosanus Shiraki (Blattodea: Termitidae) and Coptotermes formosanus Shiraki (Blattodea: Rhinotermitidae) sampled from sugarcane fields (high sugar) or pine tree forests (no free sugar) were sequenced. The results verify that the prokaryotic community structures of termites could be significantly reshaped by native dietary isolation within a species. Although the most dominant phyla are convergent in all samples, their relative abundances in these two termite species exhibited a reverse variation pattern when the termite hosts were fed on the high-sugar diet. Furthermore, we showed that the taxonomic composition of the dominant phyla at the family or genus level differentiate depending on the diet and the host phylogeny. We hypothesize that the flexible bacterial assemblages at low taxonomic level might exert variable functional collaboration to accommodate to high-sugar diet. In addition, the functional predictions of Tax4Fun suggest a stable metabolic functional structure of the microbial communities of the termites in both different diet habitats and taxonomy. We propose that the symbiotic bacterial community in different host termites developed a different functional synergistic pattern, which may be essential to maintain the stability of the overall metabolic function for the survival of termites.

Laccase Properties, Physiological Functions, and Evolution

Discovered in 1883, laccase is one of the first enzymes ever described. Now, after almost 140 years of research, it seems that this copper-containing protein with a number of unique catalytic properties is widely distributed across all kingdoms of life. Laccase belongs to the superfamily of multicopper oxidases (MCOs)—a group of enzymes comprising many proteins with different substrate specificities and diverse biological functions. The presence of cupredoxin-like domains allows all MCOs to reduce oxygen to water without producing harmful byproducts. This review describes structural characteristics and plausible evolution of laccase in different taxonomic groups. The remarkable catalytic abilities and broad substrate specificity of laccases are described in relation to other copper-containing MCOs. Through an exhaustive analysis of laccase roles in different taxa, we find that this enzyme evolved to serve an important, common, and protective function in living systems.

The de novo transcriptome of workers head of the higher group termite Globitermes sulphureus Haviland (Blattodea: Termitidae)

The subterranean termite Globitermus sulphureus is an important Southeast Asian pest with limited genomic resources that causes damages to agriculture crops and building structures. Therefore, the main goal of this study was to survey the G. sulphureus transcriptome composition. Here, we performed de novo transcriptome for G. sulphureus workers’ heads using Illumina HiSeq paired-end sequencing technology. A total of 88, 639, 408 clean reads were collected and assembled into 243, 057 transcripts and 193, 344 putative genes. The transcripts were annotated with the Trinotate pipeline. In total, 27, 061 transcripts were successfully annotated using BLASTX against the SwissProt database and 17, 816 genes were assigned to 47, 598 GO terms. We classified 14, 223 transcripts into COG classification, resulting in 25 groups of functional annotations. Next, a total of 12, 194 genes were matched in the KEGG pathway and 392 metabolic pathways were predicted based on the annotation. Moreover, we detected two endogenous cellulases in the sequences. The RT-qPCR analysis showed that there were significant differences in the expression levels of two genes β-glucosidase and endo-β-1,4-glucanase between worker and soldier heads of G. sulphureus. This is the first study to characterize the complete head transcriptome of a higher termite G. sulphureus using a high-throughput sequencing. Our study may provide an overview and comprehensive molecular resource for comparative studies of the transcriptomics and genomics of termites.

Effect of Diet on the Enteric Microbiome of the Wood-Eating Catfish Panaque nigrolineatus

Wood is consistently found in high levels in the gastrointestinal tract of the Amazonian catfish Panaque nigrolineatus, which, depending on environmental conditions, can switch between xylivorous and detritivorous dietary strategies. This is highly unusual among primary wood consumers and provides a unique system to examine the effect of dietary change in a xylivorous system. In this study, microbiome and predictive metagenomic analyses were performed for P. nigrolineatus fed either wood alone or a less refractory mixed diet containing wood and plant nutrition. While diet had an impact on enteric bacterial community composition, there was a high degree of interindividual variability. Members of the Proteobacteria and Planctomycetes were ubiquitous and dominated most communities; Bacteroidetes, Fusobacteria, Actinobacteria, and Verrucomicrobia also contributed in a tissue and diet-specific manner. Although predictive metagenomics revealed functional differences between communities, the relative abundance of predicted lignocellulose-active enzymes remained similar across diets. The microbiomes from both diets appeared highly adapted for hemicellulose hydrolysis as the predicted metagenomes contained several classes of hemicellulases and lignin-modifying enzymes. Enteric communities from both diets appeared to lack the necessary cellobiohydrolases for efficient cellulose hydrolysis, suggesting that cellobiose is not the primary source of dietary carbon for the fish. Our findings suggest that the P. nigrolineatus gut environment selects for an enteric community based on function, rather than a vertically transferred symbiotic relationship. This functional selection strategy may provide an advantage to an organism that switches between dietary strategies to survive a highly variable environment.

The ant Lasius niger is a new source of bacterial enzymes with biotechnological potential for bleaching dye

Industrial synthetic dyes cause health and environmental problems. This work describes the isolation of 84 bacterial strains from the midgut of the Lasius niger ant and the evaluation of their potential application in dye bioremediation. Strains were identified and classified as judged by rRNA 16S. The most abundant isolates were found to belong to Actinobacteria (49%) and Firmicutes (47.2%). We analyzed the content in laccase, azoreductase and peroxidase activities and their ability to degrade three known dyes (azo, thiazine and anthraquinone) with different chemical structures. Strain Ln26 (identified as Brevibacterium permense) strongly decolorized the three dyes tested at different conditions. Strain Ln78 (Streptomyces ambofaciens) exhibited a high level of activity in the presence of Toluidine Blue (TB). It was determined that 8.5 was the optimal pH for these two strains, the optimal temperature conditions ranged between 22 and 37 °C, and acidic pHs and temperatures around 50 °C caused enzyme inactivation. Finally, the genome of the most promising candidate (Ln26, approximately 4.2 Mb in size) was sequenced. Genes coding for two DyP-type peroxidases, one laccase and one azoreductase were identified and account for the ability of this strain to effectively oxidize a variety of dyes with different chemical structures.

Carbon ecology of termite gut and phenol degradation by a bacterium isolated from the gut of termite

Metagenomics and transcriptomics have had some success analyzing community and functional ecology of the termite gut, but carbon utilization ecology and the effect of diet on the gut community are not well understood. This study was done to determine the effect of three hardwood tree types, oak (Quercus spp.), red maple (Acer rubrum), and tupelo (Nyssa aquatica) on the termite species, Reticulitermes flavipes in the family Rhinotermitidae. Termite abdomen homogenates were incubated on agar plates containing three common carbon sources in the termite gut, namely, acetate, cellobiose, and phenol under aerobic and anaerobic conditions. Bacterial growth was higher on cellobiose than any other carbon source. Higher bacterial growth on cellobiose was observed from termite colonies feeding on oak than on phenol from the other two wood types. The difference between aerobic and anaerobic conditions was not significant. A bacterium, Acinetobacter tandoii isolated and identified from our previous study was subjected to high concentrations of phenol as the sole carbon source and this bacterium was able to degrade phenol concentration up to 600 mg/L.

Multi-metal tolerance of von Willebrand factor type D domain isolated from metal contaminated site by metatranscriptomics approach

Environmental pollution through heavy metals is an upcoming universal problem that relentlessly endangers human health, biodiversity and ecosystems. Hence remediating these heavy metal pollutants from the environment by engineering soil microbiome through metatranscriptomics is befitting reply. In the present investigation, we have constructed size fractionated cDNA libraries from eukaryotic mRNA of cadmium (Cd) contaminated soil and screened for Cd tolerant genes by yeast complementation system by using Cd sensitive ycf1^Δ mutant. We are reporting one of the transformants PLCe10 (from library C, 1-4 kb) with potential tolerance towards Cd toxicity (40 μM-80 μM). Sequence analysis of PLCe10 transcript showed homology to von Willebrand factor type D domain (VWD) of vitellogenin-6 of Ascaris suum encoding 338 amino acids peptide. qPCR analysis revealed that PLCe10 induced in presence of Cd (32 fold) and also accumulated maximum amount of Cd at 60 μM Cd. This cDNA was further tested for its tolerance against other heavy metals like copper (Cu), zinc (Zn) and cobalt (Co). Heterologous complementation assays of cDNA PLCe10 showed a range of tolerance to Cu (150 μM-500 μM), Zn (10 mM-12 mM) and Co (2-4 mM). Results of the present study suggest that cDNA PLCe10 is one of the functional eukaryotic heavy metal tolerant genes present among the soil microbial community and could be exploited to rehabilitate metal contaminated sites.

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

The termite gut is an efficient decomposer of polyphenol-rich diets, such as lignocellulosic biomasses, and it has been proposed that non-enzymatic oxidative mechanisms could be involved with the digestive process in these animals. However, oxidant levels are completely unknown in termites, as well as protective mechanisms against oxidative damage to the termite gut and its microbiota. As the first step in investigating the role oxidants plays in termite gut physiology, this work presents oxidant levels, antioxidant enzymatic defenses, cell renewal and microbiota abundance along the litter-feeding termite Cornitermes cumulans gut compartments (foregut, midgut, mixed segment and hindgut p1, p3, p4, and p5 segments) and salivary glands. The results show variable levels of oxidants along the C. cumulans gut, the production of antioxidant enzymes, gut cell renewal as potential defenses against oxidative injuries and the profile of microbiota distribution (being predominantly inverse to oxidant levels). In this fashion, the oxidative challenges imposed by polyphenol-rich diet seem to be circumvented by the C. cumulans gut, ensuring efficiency of the digestive process together with preservation of tissue homoeostasis and microbiota growth. These results present new insights into the physicochemical properties of the gut in a litter-feeding termite, expanding our view in relation to termites’ digestive physiology.

Functional metagenomics reveals abundant polysaccharide-degrading gene clusters and cellobiose utilization pathways within gut microbiota of a wood-feeding higher termite

Plant cell-wall polysaccharides constitute the most abundant but recalcitrant organic carbon source in nature. Microbes residing in the digestive tract of herbivorous bilaterians are particularly efficient at depolymerizing polysaccharides into fermentable sugars and play a significant support role towards their host's lifestyle. Here, we combine large-scale functional screening of fosmid libraries, shotgun sequencing, and biochemical assays to interrogate the gut microbiota of the wood-feeding "higher" termite Globitermes brachycerastes. A number of putative polysaccharide utilization gene clusters were identified with multiple fibrolytic genes. Our large-scale functional screening of 50,000 fosmid clones resulted in 464 clones demonstrating plant polysaccharide-degrading activities, including 267 endoglucanase-, 24 exoglucanase-, 72 β-glucosidase-, and 101 endoxylanase-positive clones. We sequenced 173 functionally active clones and identified ~219 genes encoding putative carbohydrate-active enzymes (CAZymes) targeting cellulose, hemicellulose and pectin. Further analyses revealed that 68 of 154 contigs encode one or more CAZyme, which includes 35 examples of putative saccharolytic operons, suggesting that clustering of CAZymes is common in termite gut microbial inhabitants. Biochemical characterization of a representative xylanase cluster demonstrated that constituent enzymes exhibited complementary physicochemical properties and saccharolytic capabilities. Furthermore, diverse cellobiose-metabolizing enzymes include β-glucosidases, cellobiose phosphorylases, and phopho-6-β-glucosidases were identified and functionally verified, indicating that the termite gut micro-ecosystem utilizes diverse metabolic pathways to interconnect hydrolysis and central metabolism. Collectively, these results provide an in-depth view of the adaptation and digestive strategies employed by gut microbiota within this tiny-yet-efficient host-associated ecosystem.

Screening of 57 Candidate Double-Stranded RNAs for Insecticidal Activity Against the Pest Termite Reticulitermes flavipes (Isoptera: Rhinotermitidae)

RNA interference insecticides have received increasing attention in recent years due to their classification as a reduced-risk biopesticide and their proposed faster path to registration compared with conventional synthetic insecticides. The goal of this study was to synthesize and compare efficacy of 62 double-stranded RNAs (dsRNAs) from 31 target genes against the pest termite species, Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae). Fifty-seven dsRNAs of ~125 base pairs each were successfully synthesized. First-tier screens using a combination immersion/feeding assay revealed 10 top candidates and also that dsRNAs coming from synthesis reactions with 80-90× yields were the most effective. Follow-up studies using uptake enhancers in combination with top candidate dsRNAs were unsuccessful. Subsequent concentration range feeding assays on the top candidates revealed two lead termiticidal dsRNAs (3' Hexamerin-2 and 3' Glycosyl Hydrolase Family [GHF] 9-2 cellulase) and another that enhanced feeding (5' GHF9-2 cellulase). Testing a matrix of combinations of these three dsRNAs revealed ultimately that the most consistently effective dsRNA combination was the 3' Hexamerin-2 + 3' GHF9-2 cellulase dsRNA combination. These results provide new information on candidate termiticidal dsRNAs and some apparent factors that have a bearing on their efficacy. Despite these successes, further research and development will be necessary to move dsRNA termiticides from pest management theory to real-world application.

Hemocyanin facilitates lignocellulose digestion by wood-boring marine crustaceans

Woody (lignocellulosic) plant biomass is an abundant renewable feedstock, rich in polysaccharides that are bound into an insoluble fiber composite with lignin. Marine crustacean woodborers of the genus Limnoria are among the few animals that can survive on a diet of this recalcitrant material without relying on gut resident microbiota. Analysis of fecal pellets revealed that Limnoria targets hexose-containing polysaccharides (mainly cellulose, and also glucomannans), corresponding with the abundance of cellulases in their digestive system, but xylans and lignin are largely unconsumed. We show that the limnoriid respiratory protein, hemocyanin, is abundant in the hindgut where wood is digested, that incubation of wood with hemocyanin markedly enhances its digestibility by cellulases, and that it modifies lignin. We propose that this activity of hemocyanins is instrumental to the ability of Limnoria to feed on wood in the absence of gut symbionts. These findings may hold potential for innovations in lignocellulose biorefining.

More than the "Killer Trait": Infection with the Bacterial Endosymbiont Caedibacter taeniospiralis Causes Transcriptomic Modulation in Paramecium Host

Endosymbiosis is a widespread phenomenon and hosts of bacterial endosymbionts can be found all-over the eukaryotic tree of life. Likely, this evolutionary success is connected to the altered phenotype arising from a symbiotic association. The potential variety of symbiont’s contributions to new characteristics or abilities of host organisms are largely unstudied. Addressing this aspect, we focused on an obligate bacterial endosymbiont that confers an intraspecific killer phenotype to its host. The symbiosis between Paramecium tetraurelia and Caedibacter taeniospiralis, living in the host’s cytoplasm, enables the infected paramecia to release Caedibacter symbionts, which can simultaneously produce a peculiar protein structure and a toxin. The ingestion of bacteria that harbor both components leads to the death of symbiont-free congeners. Thus, the symbiosis provides Caedibacter-infected cells a competitive advantage, the “killer trait.” We characterized the adaptive gene expression patterns in symbiont-harboring Paramecium as a second symbiosis-derived aspect next to the killer phenotype. Comparative transcriptomics of infected P. tetraurelia and genetically identical symbiont-free cells confirmed altered gene expression in the symbiont-bearing line. Our results show up-regulation of specific metabolic and heat shock genes whereas down-regulated genes were involved in signaling pathways and cell cycle regulation. Functional analyses to validate the transcriptomics results demonstrated that the symbiont increases host density hence providing a fitness advantage. Comparative transcriptomics shows gene expression modulation of a ciliate caused by its bacterial endosymbiont thus revealing new adaptive advantages of the symbiosis. Caedibacter taeniospiralis apparently increases its host fitness via manipulation of metabolic pathways and cell cycle control.

Lignocellulose degradation at the holobiont level: teamwork in a keystone soil invertebrate

BACKGROUND

Woodlice are recognized as keystone species in terrestrial ecosystems due to their role in the decomposition of organic matter. Thus, they contribute to lignocellulose degradation and nutrient cycling in the environment together with other macroarthropods. Lignocellulose is the main component of plants and is composed of cellulose, lignin and hemicellulose. Its digestion requires the action of multiple Carbohydrate-Active enZymes (called CAZymes), typically acting together as a cocktail with complementary, synergistic activities and modes of action. Some invertebrates express a few endogenous lignocellulose-degrading enzymes but in most species, an efficient degradation and digestion of lignocellulose can only be achieved through mutualistic associations with endosymbionts. Similar to termites, it has been suspected that several bacterial symbionts may be involved in lignocellulose degradation in terrestrial isopods, by completing the CAZyme repertoire of their hosts.

RESULTS

To test this hypothesis, host transcriptomic and microbiome shotgun metagenomic datasets were obtained and investigated from the pill bug Armadillidium vulgare. Many genes of bacterial and archaeal origin coding for CAZymes were identified in the metagenomes of several host tissues and the gut content of specimens from both laboratory lineages and a natural population of A. vulgare. Some of them may be involved in the degradation of cellulose, hemicellulose, and lignin. Reconstructing a lignocellulose-degrading microbial community based on the prokaryotic taxa contributing relevant CAZymes revealed two taxonomically distinct but functionally redundant microbial communities depending on host origin. In parallel, endogenous CAZymes were identified from the transcriptome of the host and their expression in digestive tissues was demonstrated by RT-qPCR, demonstrating a complementary enzyme repertoire for lignocellulose degradation from both the host and the microbiome in A. vulgare.

CONCLUSIONS

Our results provide new insights into the role of the microbiome in the evolution of terrestrial isopods and their adaptive radiation in terrestrial habitats.

Metatranscriptome analysis of the intestinal microorganisms in Pardosa pseudoannulata in response to cadmium stress

Cadmium (Cd) generates a variety of physiological and ecological toxicity to spiders. However, little is known about the effects of Cd on symbiotic bacteria of spiders. Metatranscriptomics is increasing our knowledge of microorganisms in environment. To better understand the impact of Cd on the symbiotic bacteria of spiders, we generated and compared the metatranscriptomes of the intestinal microorganisms of Pardosa pseudoannulata with and without Cd stress. The community structure of intestinal microorganisms in P. pseudoannulata was composed of 4 kingdoms, namely bacteria, viruses, eukaryotes and archaea, including 46 phyla, 97 classes, 184 orders, 339 families, 470 genera, and 598 species. The abundance of eukaryotes, bacteria and viruses was decreased by 0.14%, 1.22% and 2.52% respectively while the archaea was increased by 99.16% when under Cd stress. We identified 1519 differentially expressed genes (DEGs), including 770 up-regulated and 749 down-regulated genes. The results of KEGG annotation revealed that the expression of genes that are involved in the carbon metabolism, protein and amino acid metabolism and synthesis, glucose metabolism, oxidative phosphorylation, and glutathione metabolism were influenced by Cd. Collectively, these findings showed that Cd significantly impacted the community structure and expression of related functional genes of intestinal microorganisms in P. pseudoannulata.

Characterization of a laccase from a wood-feeding termite, Coptotermes formosanus

Coptotermes formosanus Shiraki is a wood-feeding termite which secretes a series of lignolytic and cellulolytic enzymes for woody biomass degradation. However, the lignin modification mechanism in the termite is largely elusive, and the characteristics of most lignolytic enzymes in termites remain unknown. In this study, a laccase gene lac1 from C. formosanus was heterogeneously expressed in insect Sf9 cells. The purified Lac1 showed strong activities toward hydroquinone (305 mU/mg) and 2,6-dimethoxyphenol (2.9 mU/mg) with low K_m values, but not veratryl alcohol or 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid). Lac1 could function well from pH 4.5 to 7.5, and its activity was significantly inhibited by H₂ O₂ at above 4.85 mmol/L (P < 0.01). In addition, the lac1 gene was found to be mainly expressed in the salivary glands and foregut of C. formosanus, and seldom in the midgut or hindgut. These findings suggested that Lac1 is a phenol-oxidizing laccase like RflacA and RflacB from termite Reticulitermes flavipes, except that Lac1 was found to be more efficient in phenol oxidation, and it did not require H₂ O₂ for its function. It is suspected that this kind of termite laccase might only be able to directly oxidize low redox-potential substrates, and the high redox-potential groups in lignin might be oxidized by other enzymes in the termite or by using the Fenton reaction.

Transcriptome analysis of the digestive system of a wood-feeding termite (Coptotermes formosanus) revealed a unique mechanism for effective biomass degradation

BACKGROUND

Wood-feeding termite, Coptotermes formosanus Shiraki, represents a highly efficient system for biomass deconstruction and utilization. However, the detailed mechanisms of lignin modification and carbohydrate degradation in this system are still largely elusive.

RESULTS

In order to reveal the inherent mechanisms for efficient biomass degradation, four different organs (salivary glands, foregut, midgut, and hindgut) within a complete digestive system of a lower termite, C. formosanus, were dissected and collected. Comparative transcriptomics was carried out to analyze these organs using high-throughput RNA sequencing. A total of 71,117 unigenes were successfully assembled, and the comparative transcriptome analyses revealed significant differential distributions of GH (glycosyl hydrolase) genes and auxiliary redox enzyme genes in different digestive organs. Among the GH genes in the salivary glands, the most abundant were GH9, GH22, and GH1 genes. The corresponding enzymes may have secreted into the foregut and midgut to initiate the hydrolysis of biomass and to achieve a lignin-carbohydrate co-deconstruction system. As the most diverse GH families, GH7 and GH5 were primarily identified from the symbiotic protists in the hindgut. These enzymes could play a synergistic role with the endogenous enzymes from the host termite for biomass degradation. Moreover, twelve out of fourteen genes coding auxiliary redox enzymes from the host termite origin were induced by the feeding of lignin-rich diets. This indicated that these genes may be involved in lignin component deconstruction with its redox network during biomass pretreatment.

CONCLUSION

These findings demonstrate that the termite digestive system synergized the hydrolysis and redox reactions in a programmatic process, through different parts of its gut system, to achieve a maximized utilization of carbohydrates. The detailed unique mechanisms identified from the termite digestive system may provide new insights for advanced design of future biorefinery.

Biological strategies for enhanced hydrolysis of lignocellulosic biomass during anaerobic digestion: Current status and future perspectives

Lignocellulosic biomass is the most abundant renewable bioresource on earth. In lignocellulosic biomass, the cellulose and hemicellulose are bound with lignin and other molecules to form a complex structure not easily accessible to microbial degradation. Anaerobic digestion (AD) of lignocellulosic biomass with a focus on improving hydrolysis, the rate limiting step in AD of lignocellulosic feedstocks, has received considerable attention. This review highlights challenges with AD of lignocellulosic biomass, factors contributing to its recalcitrance, and natural microbial ecosystems, such as the gastrointestinal tracts of herbivorous animals, capable of performing hydrolysis efficiently. Biological strategies that have been evaluated to enhance hydrolysis of lignocellulosic biomass include biological pretreatment, co-digestion, and inoculum selection. Strategies to further improve these approaches along with future research directions are outlined with a focus on linking studies of microbial communities involved in hydrolysis of lignocellulosics to process engineering.

RNA interference unveils the importance of Pseudotrichonympha grassii cellobiohydrolase, a protozoan exoglucanase, in termite cellulose degradation

Based on prior work, a cellulase from glycosyl hydrolase family 7 (GHF7) was identified and found to be expressed at a high level in Coptotermes formosanus. To determine the function of GHF7 family members in vivo, we used RNA interference (RNAi) to functionally analyse the exoglucanase gene Pseudotrichonympha grassii cellobiohydrolase gene (PgCBH), which was highly expressed in Pseudotrichonympha grassii, a flagellate found in the hindgut of C. formosanus. In this study, the expression level of PgCBH was down-regulated by RNAi, causing the death of P. grassii, but no effect was observed for other flagellates found in C. formosanus. RNAi also resulted in significantly reduced exoglucanase activity, and no effect was observed for endoglucanase and β-glucosidase activities. This result demonstrated that the PgCBH gene plays a role in the protist lignocellulolytic process and is also important for host survival. PgCBH can be used as a target gene and has potential as a bioinsecticide for use against termites.

Discovering Protein-Coding Genes from the Environment: Time for the Eukaryotes?

Eukaryotic microorganisms from diverse environments encompass a large number of taxa, many of them still unknown to science. One strategy to mine these organisms for genes of biotechnological relevance is to use a pool of eukaryotic mRNA directly extracted from environmental samples. Recent reports demonstrate that the resulting metatranscriptomic cDNA libraries can be screened by expression in yeast for a wide range of genes and functions from many of the different eukaryotic taxa. In combination with novel emerging high-throughput technologies, we anticipate that this approach should contribute to exploring the functional diversity of the eukaryotic microbiota.