A GHF7 cellulase from the protist symbiont community of Reticulitermes flavipes enables more efficient lignocellulose processing by host enzymes

The crystal structure of RsSymEG1 reveals a unique form of smaller GH7 endoglucanases alongside GH7 cellobiohydrolases in protist symbionts of termites

Glycoside hydrolase family 7 (GH7) cellulases are key enzymes responsible for carbon cycling on earth through their role in cellulose degradation and constitute highly important industrial enzymes as well. Although these enzymes are found in a wide variety of evolutionarily distant organisms across eukaryotes, they exhibit remarkably conserved features within two groups: exo-acting cellobiohydrolases and endoglucanases. However, recently reports have emerged of a separate clade of GH7 endoglucanases from protist symbionts of termites that are 60-80 amino acids shorter. In this work, we describe the first crystal structure of a short GH7 endoglucanase, RsSymEG1, from a symbiont of the lower termite Reticulitermes speratus. A more open flat surface and shorter loops around the non-reducing end of the cellulose-binding cleft indicate enhanced access to cellulose chains on the surface of cellulose microfibrils. Additionally, when comparing activities on polysaccharides to a typical fungal GH7 endoglucanase (Trichoderma longibrachiatum Cel7B), RsSymEG1 showed significantly faster initial hydrolytic activity. We also examine the prevalence and diversity of GH7 enzymes that the symbionts provide to the termite host, compare overall structures and substrate binding between cellobiohydrolase and long and short endoglucanase, and highlight the presence of similar short GH7s in other organisms.

First evidence of a horizontally-acquired GH-7 cellobiohydrolase from a longhorned beetle genome

Xylophagous larvae of longhorned beetles (Coleoptera; Cerambycidae) efficiently break down polysaccharides of the plant cell wall, which make the bulk of their food, using a range of carbohydrate-active enzymes (CAZymes). In this study, we investigated the function and evolutionary history of the first identified example of insect-encoded members of glycoside hydrolase family 7 (GH7) derived from the Lamiinae Exocentrus adspersus. The genome of this beetle contained two genes encoding GH7 proteins located in tandem and flanked by transposable elements. Phylogenetic analysis revealed that the GH7 sequences of E. adspersus were closely related to those of Ascomycete fungi, suggesting that they were acquired through horizontal gene transfer (HGT) from fungi. However, they were more distantly related to those encoded by genomes of Crustacea and of protist symbionts of termites and cockroaches, supporting that the same enzyme family was recruited several times independently in Metazoa during the course of their evolution. The recombinant E. adspersus GH7 was found to primarily break down cellulose polysaccharides into cellobiose, indicating that it is a cellobiohydrolase, and could also use smaller cellulose oligomers as substrates. Additionally, the cellobiohydrolase activity was boosted by the presence of calcium chloride. Our findings suggest that the combination of GH7 cellobiohydrolases with other previously characterized endo-β-1,4-glucanases and β-glucosidases allows longhorned beetles like E. adspersus to efficiently break down cellulose into monomeric glucose.

Impact of Wood Age on Termite Microbial Assemblages

The decomposition of wood and detritus is challenging to most macroscopic organisms due to the recalcitrant nature of lignocellulose. Moreover, woody plants often protect themselves by synthesizing toxic or nocent compounds which infuse their tissues. Termites are essential wood decomposers in warmer terrestrial ecosystems and, as such, they have to cope with high concentrations of plant toxins in wood. In this paper, we evaluated the influence of wood age on the gut microbial (bacterial and fungal) communities associated with the termites Reticulitermes flavipes (Rhinotermitidae) (Kollar, 1837) and Microcerotermes biroi (Termitidae) (Desneux, 1905). We confirmed that the secondary metabolite concentration decreased with wood age. We identified a core microbial consortium maintained in the gut of R. flavipes and M. biroi and found that its diversity and composition were not altered by the wood age. Therefore, the concentration of secondary metabolites had no effect on the termite gut microbiome. We also found that both termite feeding activities and wood age affect the wood microbiome. Whether the increasing relative abundance of microbes with termite activities is beneficial to the termites is unknown and remains to be investigated. IMPORTANCE Termites can feed on wood thanks to their association with their gut microbes. However, the current understanding of termites as holobiont is limited. To our knowledge, no studies comprehensively reveal the influence of wood age on the termite-associated microbial assemblage. The wood of many tree species contains high concentrations of plant toxins that can vary with their age and may influence microbes. Here, we studied the impact of Norway spruce wood of varying ages and terpene concentrations on the microbial communities associated with the termites Reticulitermes flavipes (Rhinotermitidae) and Microcerotermes biroi (Termitidae). We performed a bacterial 16S rRNA and fungal ITS2 metabarcoding study to reveal the microbial communities associated with R. flavipes and M. biroi and their impact on shaping the wood microbiome. We noted that a stable core microbiome in the termites was unaltered by the feeding substrate, while termite activities influenced the wood microbiome, suggesting that plant secondary metabolites have negligible effects on the termite gut microbiome. Hence, our study shed new insights into the termite-associated microbial assemblage under the influence of varying amounts of terpene content in wood and provides a groundwork for future investigations for developing symbiont-mediated termite control measures.

Oxidative cleavage of polysaccharides by a termite-derived superoxide dismutase boosts the degradation of biomass by glycoside hydrolases

Wood-feeding termites effectively degrade plant biomass through enzymatic degradation. Despite their high efficiencies, however, individual glycoside hydrolases isolated from termites and their symbionts exhibit anomalously low effectiveness in lignocellulose degradation, suggesting hereto unknown enzymatic activities in their digestome. Herein, we demonstrate that an ancient redox-active enzyme encoded by the lower termite Coptotermes gestroi, a Cu/Zn superoxide dismutase (CgSOD-1), plays a previously unknown role in plant biomass degradation. We show that CgSOD-1 transcripts and peptides are up-regulated in response to an increased level of lignocellulose recalcitrance and that CgSOD-1 localizes in the lumen of the fore- and midguts of C. gestroi together with termite main cellulase, CgEG-1-GH9. CgSOD-1 boosts the saccharification of polysaccharides by CgEG-1-GH9. We show that the boosting effect of CgSOD-1 involves an oxidative mechanism of action in which CgSOD-1 generates reactive oxygen species that subsequently cleave the polysaccharide. SOD-type enzymes constitute a new addition to the growing family of oxidases, ones which are up-regulated when exposed to recalcitrant polysaccharides, and that are used by Nature for biomass degradation.

Three endogenous cellulases from termite, Reticulitermes speratus KMT001

Among termites, lower termites need symbiotic microorganisms in the digestive tract for digestion and cellulose metabolism. In this symbiotic relationship, the decomposition of cellulose is initiated by endoglucanase in termite salivary glands and completed by β-glycosidase of symbiotic microorganisms in the hindgut. The expression of β-glycosidase in lower termites has been reported in recent studies. The expression of two endoglucanases and one β-glycosidase gene related to cellulose degradation was identified in Reticulitermes speratus, a lower termite, through transcriptomic analysis. The proposed enzyme activities of three identified cellulose degradation genes were confirmed by heterologous expression in Escherichia coli. In addition to the endoglucanase expressed in the salivary gland, additional endoglucanase and β-glycosidase genes suggest that R. speratus performs the overall cellulose digestion using its own enzymes at all stages.

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.

On the roles of AA15 lytic polysaccharide monooxygenases derived from the termite Coptotermes gestroi

Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes which catalyze the oxidative cleavage of polysaccharides. LPMOs belonging to family 15 in the Auxiliary Activity (AA) class from the Carbohydrate-Active Enzyme database are found widespread across the Tree of Life, including viruses, algae, oomycetes and animals. Recently, two AA15s from the firebrat Thermobia domestica were reported to have oxidative activity, one towards cellulose or chitin and the other towards chitin, signalling that AA15 LPMOs from insects potentially have different biochemical functions. Herein, we report the identification and characterization of two family AA15 members from the lower termite Coptotermes gestroi. Addition of Cu(II) to CgAA15a or CgAA15b had a thermostabilizing effect on both. Using ascorbate and O₂ as co-substrates, CgAA15a and CgAA15b were able to oxidize chitin, but showed no activity on celluloses, xylan, xyloglucan and starch. Structural models indicate that the LPMOs from C. gestroi (CgAA15a/CgAA15b) have a similar fold but exhibit key differences in the catalytic site residues when compared to the cellulose/chitin-active LPMO from T. domestica (TdAA15a), especially the presence of a non-coordinating phenylalanine nearby the Cu ion in CgAA15a/b, which appears as a tyrosine in the active site of TdAA15a. Despite the overall similarity in protein folds, however, mutation of the active site phenylalanine in CgAA15a to a tyrosine did not expanded the enzymatic specificity from chitin to cellulose. Our data show that CgAA15a/b enzymes are likely not involved in lignocellulose digestion but might play a role in termite developmental processes as well as on chitin and nitrogen metabolisms.

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.

The genome of pest Rhynchophorus ferrugineus reveals gene families important at the plant-beetle interface

The red palm weevil, Rhynchophorus ferrugineus, infests palm plantations, leading to large financial losses and soil erosion. Pest-host interactions are poorly understood in R. ferrugineus, but the analysis of genetic diversity and pest origins will help advance efforts to eradicate this pest. We sequenced the genome of R. ferrugineus using a combination of paired-end Illumina sequencing (150 bp), Oxford Nanopore long reads, 10X Genomics and synteny analysis to produce an assembly with a scaffold N50 of ~60 Mb. Structural variations showed duplication of detoxifying and insecticide resistance genes (e.g., glutathione S-transferase, P450, Rdl). Furthermore, the evolution of gene families identified those under positive selection including one glycosyl hydrolase (GH16) gene family, which appears to result from horizontal gene transfer. This genome will be a valuable resource to understand insect evolution and behavior and to allow the genetic modification of key genes that will help control this pest.

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

BACKGROUND

The bamboo weevil Cyrtotrachelus buqueti, which is considered a pest species, damages bamboo shoots via its piercing-sucking mode of feeding. C. buqueti is well known for its ability to transform bamboo shoot biomass into nutrients and energy for growth, development and reproduction with high specificity and efficacy of bioconversion. Woody bamboo is a perennial grass that is a potential feedstock for lignocellulosic biomass because of its high growth rate and lignocellulose content. To verify our hypothesis that C. buqueti efficiently degrades bamboo lignocellulose, we assessed the bamboo lignocellulose-degrading ability of this insect through RNA sequencing for identifying a potential route for utilisation of bamboo biomass.

RESULTS

Analysis of carbohydrate-active enzyme (CAZyme) family genes in the developmental transcriptome of C. buqueti revealed 1082 unigenes, including 55 glycoside hydrolases (GH) families containing 309 GHs, 51 glycosyltransferases (GT) families containing 329 GTs, 8 carbohydrate esterases (CE) families containing 174 CEs, 6 polysaccharide lyases (PL) families containing 11 PLs, 8 auxiliary activities (AA) families containing 131 enzymes with AAs and 17 carbohydrate-binding modules (CBM) families containing 128 CBMs. We used weighted gene co-expression network analysis to analyse developmental RNA sequencing data, and 19 unique modules were identified in the analysis. Of these modules, the expression of MEyellow module genes was unique and the module included numerous CAZyme family genes. CAZyme genes in this module were divided into two groups depending on whether gene expression was higher in the adult/larval stages or in the egg/pupal stages. Enzyme assays revealed that cellulase activity was highest in the midgut whereas lignin-degrading enzyme activity was highest in the hindgut, consistent with findings from intestinal gene expression studies. We also analysed the expression of CAZyme genes in the transcriptome of C. buqueti from two cities and found that several genes were also assigned to CAZyme families. The insect had genes and enzymes associated with lignocellulose degradation, the expression of which differed with developmental stage and intestinal region.

CONCLUSION

Cyrtotrachelus buqueti exhibits lignocellulose degradation-related enzymes and genes, most notably CAZyme family genes. CAZyme family genes showed differences in expression at different developmental stages, with adults being more effective at cellulose degradation and larvae at lignin degradation, as well as at different regions of the intestine, with the midgut being more cellulolytic than the hindgut. This degradative system could be utilised for the bioconversion of bamboo lignocellulosic biomass.

A meta-analysis testing eusocial co-option theories in termite gut physiology and symbiosis

The termite gut accomplishes key physiologic functions that underlie termite symbiosis and sociality. However, potential candidate functions of the host-symbiont holobiome have not yet been explored across seemingly divergent processes such as digestion, immunity, caste differentiation, and xenobiotic tolerance. This study took a meta-analysis approach for concurrently studying host and symbiont gut metatranscriptome responses of the lower termite Reticulitermes flavipes, which has ancestral characteristics and hosts a diverse mix of eukaryotic and bacterial symbionts. Thirteen treatments were compared from 5 categories (dietary, social, hormonal, immunological, and xenobiotic), revealing 3 main insights. First, each of the 5 tested colonies had distinct magnitudes of transcriptome response, likely as a result of unique symbiont profiles, which highlights the uniqueness of individual termite colonies. Second, after normalization to standardize colony response magnitudes, unique treatment-linked metatranscriptome topologies became apparent. Third, despite colony and topology differences, 4 co-opted master genes emerged that were universally responsive across diverse treatments. These master genes encode host functions related to protein translation and symbiont functions related to protein degradation and pore formation in microbial cell walls. Three of the 4 master genes were from co-evolved protist symbionts, highlighting potentially co-evolved roles for gut symbiota in coordinating functional responses of the collective host-symbiont holobiome. Lastly, for host genes identified, these results provide annotations of recent termite genome sequences. By revealing conserved domain genes, as well as apparent roles for gut symbiota in holobiome regulation, this study provides new insights into co-opted eusocial genes and symbiont roles in termite sociobiology.

Expanding the Knowledge on Lignocellulolytic and Redox Enzymes of Worker and Soldier Castes from the Lower Termite Coptotermes gestroi

Termites are considered one of the most efficient decomposers of lignocelluloses on Earth due to their ability to produce, along with its microbial symbionts, a repertoire of carbohydrate-active enzymes (CAZymes). Recently, a set of Pro-oxidant, Antioxidant, and Detoxification enzymes (PAD) were also correlated with the metabolism of carbohydrates and lignin in termites. The lower termite Coptotermes gestroi is considered the main urban pest in Brazil, causing damage to wood constructions. Recently, analysis of the enzymatic repertoire of C. gestroi unveiled the presence of different CAZymes. Because the gene profile of CAZy/PAD enzymes endogenously synthesized by C. gestroi and also by their symbiotic protists remains unclear, the aim of this study was to explore the eukaryotic repertoire of these enzymes in worker and soldier castes of C. gestroi. Our findings showed that worker and soldier castes present similar repertoires of CAZy/PAD enzymes, and also confirmed that endo-glucanases (GH9) and beta-glucosidases (GH1) were the most important glycoside hydrolase families related to lignocellulose degradation in both castes. Classical cellulases such as exo-glucanases (GH7) and endo-glucanases (GH5 and GH45), as well as classical xylanases (GH10 and GH11), were found in both castes only taxonomically related to protists, highlighting the importance of symbiosis in C. gestroi. Moreover, our analysis revealed the presence of Auxiliary Activity enzyme families (AAs), which could be related to lignin modifications in termite digestomes. In conclusion, this report expanded the knowledge on genes and proteins related to CAZy/PAD enzymes from worker and soldier castes of lower termites, revealing new potential enzyme candidates for second-generation biofuel processes.

Lower Termite Associations with Microbes: Synergy, Protection, and Interplay

Lower-termites are one of the best studied symbiotic systems in insects. Their ability to feed on a nitrogen-poor, wood-based diet with help from symbiotic microbes has been under investigation for almost a century. A unique microbial consortium living in the guts of lower termites is essential for wood-feeding. Host and symbiont cellulolytic enzymes synergize each other in the termite gut to increase digestive efficiency. Because of their critical role in digestion, gut microbiota are driving forces in all aspects of termite biology. Social living also comes with risks for termites. The combination of group living and a microbe-rich habitat makes termites potentially vulnerable to pathogenic infections. However, the use of entomopathogens for termite control has been largely unsuccessful. One mechanism for this failure may be symbiotic collaboration; i.e., one of the very reasons termites have thrived in the first place. Symbiont contributions are thought to neutralize fungal spores as they pass through the termite gut. Also, when the symbiont community is disrupted pathogen susceptibility increases. These recent discoveries have shed light on novel interactions for symbiotic microbes both within the termite host and with pathogenic invaders. Lower termite biology is therefore tightly linked to symbiotic associations and their resulting physiological collaborations.

Digestion of Termiticide Bait Matrices by the Pest Termite Reticulitermes flavipes (Isoptera: Rhinotermitidae)

Termites are highly effective digesters of wood lignocellulose, which is a central factor contributing to their global status as pests of wooden structures. For the same reason, termite baits that combine cellulosic matrices with slow-acting insecticides are both effective and popular as a reduced-risk approach for termite control. This study took a novel approach for assessing digestibility of termite bait matrices and matrix components to gain potentially new insights into bait attractiveness and efficacy. The rationale behind this study is that termite baits that are more digestible should have more nutritional value to termites and thus encourage maximal feeding and trophallactic transfer of active ingredients through termite colonies. Studies were done using in vitro digestion assays with termite gut protein extracts followed by colorimetric detection of released glucose and pentose monosaccharides from test substrates. The substrates tested included two commercial bait matrices (Recruit IV and Recruit II HD), two matrix components (compressed and toasted compressed cellulose), and two natural pine woods as positive controls (southern yellow and northern pine). Overall results show equal or greater monosaccharide availability for some commercial matrices than standard pine lignocelluloses, suggesting sufficient nutritional value for the proprietary matrices. Another more prominent trend was significant intercolony variation in digestibility across substrates, possibly resulting from differences in microbiota composition, long-term diet adaptation, or both. These findings thus illuminate new nutrition-based factors that can potentially impact bait feeding, trophallactic exchange, and efficacy.

Metatranscriptomic profiles of Eastern subterranean termites, Reticulitermes flavipes (Kollar) fed on second generation feedstocks

BACKGROUND

Second generation lignocellulosic feedstocks are being considered as an alternative to first generation biofuels that are derived from grain starches and sugars. However, the current pre-treatment methods for second generation biofuel production are inefficient and expensive due to the recalcitrant nature of lignocellulose. In this study, we used the lower termite Reticulitermes flavipes (Kollar), as a model to identify potential pretreatment genes/enzymes specifically adapted for use against agricultural feedstocks.

RESULTS

Metatranscriptomic profiling was performed on worker termite guts after feeding on corn stover (CS), soybean residue (SR), or 98% pure cellulose (paper) to identify (i) microbial community, (ii) pathway level and (iii) gene-level responses. Microbial community profiles after CS and SR feeding were different from the paper feeding profile, and protist symbiont abundance decreased significantly in termites feeding on SR and CS relative to paper. Functional profiles after CS feeding were similar to paper and SR; whereas paper and SR showed different profiles. Amino acid and carbohydrate metabolism pathways were downregulated in termites feeding on SR relative to paper and CS. Gene expression analyses showed more significant down regulation of genes after SR feeding relative to paper and CS. Stereotypical lignocellulase genes/enzymes were not differentially expressed, but rather were among the most abundant/constitutively-expressed genes.

CONCLUSIONS

These results suggest that the effect of CS and SR feeding on termite gut lignocellulase composition is minimal and thus, the most abundantly expressed enzymes appear to encode the best candidate catalysts for use in saccharification of these and related second-generation feedstocks. Further, based on these findings we hypothesize that the most abundantly expressed lignocellulases, rather than those that are differentially expressed have the best potential as pretreatment enzymes for CS and SR feedstocks.

Molecular signatures of nicotinoid-pathogen synergy in the termite gut

Previous studies in lower termites revealed unexpected synergies between nicotinoid insecticides and fungal entomopathogens. The present study investigated molecular mechanisms of nicotinoid-pathogen synergy in the lower termite Reticulitermes flavipes, using the nicotinoid, imidacloprid, in combination with fungal and bacterial entomopathogens. Particular focus was placed on metatranscriptome composition and microbial dynamics in the symbiont-rich termite gut, which houses diverse mixes of protists and bacteria. cDNA microarrays containing a mix of host and protist symbiont oligonucleotides were used to simultaneously assess termite and protist gene expression. Five treatments were compared that included single challenges with sublethal doses of fungi (Metharizium anisopliae), bacteria (Serratia marcescens) or imidacloprid, and dual challenges with fungi + imidacloprid or bacteria + imidacloprid. Our findings point towards protist dysbiosis and compromised social behavior, rather than suppression of stereotypical immune defense mechanisms, as the dominant factors underlying nicotinoid-pathogen synergy in termites. Also, greater impacts observed for the fungal pathogen than for the bacterial pathogen suggest that the rich bacterial symbiont community in the R. flavipes gut (>5000 species-level phylotypes) exists in an ecological balance that effectively excludes exogenous bacterial pathogens. These findings significantly advance our understanding of antimicrobial defenses in this important eusocial insect group, as well as provide novel insights into how nicotinoids can exert deleterious effects on social insect colonies.

Quantification of symbiotic contributions to lower termite lignocellulose digestion using antimicrobial treatments

Animal-microbe co-evolution and symbiosis are broadly distributed across the animal kingdom. Insects form a myriad of associations with microbes ranging from vectoring of pathogens to intracellular, mutualistic relationships. Lower termites are key models for insect-microbe symbiosis because of the diversity, complexity and functionality of their unique tripartite symbiosis. This collaboration allows termites to live on a diet of nitrogen-poor lignocellulose. Recent functional investigations of lignocellulose digestion in lower termites have primarily focused on the contributions of the eukaryotic members of the termite holobiont (termite and protist). Here, using multiple antimicrobial treatments, we induced differing degrees of dysbiosis in the termite gut, leading to variably altered symbiont abundance and diversity, and lignocellulolytic capacity. Although protists are clearly affected by antimicrobial treatments, our findings provide novel evidence that the removal of distinct groups of bacteria partially reduces, but does not abolish, the saccharolytic potential of the termite gut holobiont. This is specifically manifested by reductions of 23-47% and 30-52% in glucose and xylose yields respectively from complex lignocellulose. Thus, all members of the lower termite holobiont (termite, protist and prokaryotes) are involved in the process of efficient, sustained lignocellulase activity. This unprecedented quantification of the relative importance of prokaryotes in this system emphasizes the collaborative nature of the termite holobiont, and the relevance of lower termites as models for inter-domain symbioses.

Omic research in termites: an overview and a roadmap

Many recent breakthroughs in our understanding of termite biology have been facilitated by "omics" research. Omic science seeks to collectively catalog, quantify, and characterize pools of biological molecules that translate into structure, function, and life processes of an organism. Biological molecules in this context include genomic DNA, messenger RNA, proteins, and other biochemicals. Other permutations of omics that apply to termites include sociogenomics, which seeks to define social life in molecular terms (e.g., behavior, sociality, physiology, symbiosis, etc.) and digestomics, which seeks to define the collective pool of host and symbiont genes that collaborate to achieve high-efficiency lignocellulose digestion in the termite gut. This review covers a wide spectrum of termite omic studies from the past 15 years. Topics covered include a summary of terminology, the various kinds of omic efforts that have been undertaken, what has been revealed, and to a degree, what the results mean. Although recent omic efforts have contributed to a better understanding of many facets of termite and symbiont biology, and have created important new resources for many species, significant knowledge gaps still remain. Crossing these gaps can best be done by applying new omic resources within multi-dimensional (i.e., functional, translational, and applied) research programs.

Termites as targets and models for biotechnology

Termites have many unique evolutionary adaptations associated with their eusocial lifestyles. Recent omics research has created a wealth of new information in numerous areas of termite biology (e.g., caste polyphenism, lignocellulose digestion, and microbial symbiosis) with wide-ranging applications in diverse biotechnological niches. Termite biotechnology falls into two categories: (a) termite-targeted biotechnology for pest management purposes, and (b) termite-modeled biotechnology for use in various industrial applications. The first category includes several candidate termiticidal modes of action such as RNA interference, digestive inhibition, pathogen enhancement, antimicrobials, endocrine disruption, and primer pheromone mimicry. In the second category, termite digestomes are deep resources for host and symbiont lignocellulases and other enzymes with applications in a variety of biomass, industrial, and processing applications. Moving forward, one of the most important approaches for accelerating advances in both termite-targeted and termite-modeled biotechnology will be to consider host and symbiont together as a single functional unit.

Protozoacidal Trojan-Horse: use of a ligand-lytic peptide for selective destruction of symbiotic protozoa within termite guts

For novel biotechnology-based termite control, we developed a cellulose bait containing freeze-dried genetically engineered yeast which expresses a protozoacidal lytic peptide attached to a protozoa-recognizing ligand. The yeast acts as a ‘Trojan-Horse’ that kills the cellulose-digesting protozoa in the termite gut, which leads to the death of termites, presumably due to inefficient cellulose digestion. The ligand targets the lytic peptide specifically to protozoa, thereby increasing its protozoacidal efficiency while protecting non-target organisms. After ingestion of the bait, the yeast propagates in the termite's gut and is spread throughout the termite colony via social interactions. This novel paratransgenesis-based strategy could be a good supplement for current termite control using fortified biological control agents in addition to chemical insecticides. Moreover, this ligand-lytic peptide system could be used for drug development to selectively target disease-causing protozoa in humans or other vertebrates.