Differential cellulolytic activity of native-form and C-terminal tagged-form cellulase derived from Coptotermes formosanus and expressed in E. coli

Plant Growth Promotion and Plant Disease Suppression Induced by Bacillus amyloliquefaciens Strain GD4a

Botrytis cinerea, the causative agent of gray mold disease (GMD), invades plants to obtain nutrients and disseminates through airborne conidia in nature. Bacillus amyloliquefaciens strain GD4a, a beneficial bacterium isolated from switchgrass, shows great potential in managing GMD in plants. However, the precise mechanism by which GD4a confers benefits to plants remains elusive. In this study, an A. thaliana-B. cinerea-B. amyloliquefaciens multiple-scale interaction model was used to explore how beneficial bacteria play essential roles in plant growth promotion, plant pathogen suppression, and plant immunity boosting. Arabidopsis Col-0 wild-type plants served as the testing ground to assess GD4a's efficacy. Additionally, bacterial enzyme activity and targeted metabolite tests were conducted to validate GD4a's potential for enhancing plant growth and suppressing plant pathogens and diseases. GD4a was subjected to co-incubation with various bacterial, fungal, and oomycete pathogens to evaluate its antagonistic effectiveness in vitro. In vivo pathogen inoculation assays were also carried out to investigate GD4a's role in regulating host plant immunity. Bacterial extracellular exudate (BEE) was extracted, purified, and subjected to untargeted metabolomics analysis. Benzocaine (BEN) from the untargeted metabolomics analysis was selected for further study of its function and related mechanisms in enhancing plant immunity through plant mutant analysis and qRT-PCR analysis. Finally, a comprehensive model was formulated to summarize the potential benefits of applying GD4a in agricultural systems. Our study demonstrates the efficacy of GD4a, isolated from switchgrass, in enhancing plant growth, suppressing plant pathogens and diseases, and bolstering host plant immunity. Importantly, GD4a produces a functional bacterial extracellular exudate (BEE) that significantly disrupts the pathogenicity of B. cinerea by inhibiting fungal conidium germination and hypha formation. Additionally, our study identifies benzocaine (BEN) as a novel small molecule that triggers basal defense, ISR, and SAR responses in Arabidopsis plants. Bacillus amyloliquefaciens strain GD4a can effectively promote plant growth, suppress plant disease, and boost plant immunity through functional BEE production and diverse gene expression.

Evolution of a Cockroach Allergen into the Major Protein of Termite Royal Jelly

Termites live in colonies, and their members belong to different castes that each have their specific role within the termite society. In well-established colonies of higher termites, the only food the founding female, the queen, receives is saliva from workers; such queens can live for many years and produce up to 10,000 eggs per day. In higher termites, worker saliva must thus constitute a complete diet and therein resembles royal jelly produced by the hypopharyngeal glands of honeybee workers that serves as food for their queens; indeed, it might as well be called termite royal jelly. However, whereas the composition of honeybee royal jelly is well established, that of worker termite saliva in higher termites remains largely unknown. In lower termites, cellulose-digesting enzymes constitute the major proteins in worker saliva, but these enzymes are absent in higher termites. Others identified a partial protein sequence of the major saliva protein of a higher termite and identified it as a homolog of a cockroach allergen. Publicly available genome and transcriptome sequences from termites make it possible to study this protein in more detail. The gene coding the termite ortholog was duplicated, and the new paralog was preferentially expressed in the salivary gland. The amino acid sequence of the original allergen lacks the essential amino acids methionine, cysteine and tryptophan, but the salivary paralog incorporated these amino acids, thus allowing it to become more nutritionally balanced. The gene is found in both lower and higher termites, but it is in the latter that the salivary paralog gene got reamplified, facilitating an even higher expression of the allergen. This protein is not expressed in soldiers, and, like the major royal jelly proteins in honeybees, it is expressed in young but not old workers.

Characterization of Siccibacter sp. Strain C2 a Novel Rhizobacterium that Enhances Tolerance of Barley to Salt Stress

Plant growth promoting rhizobacteria (PGPR) arouse an increasing interest as an eco-friendly solution for improving crop tolerance to environmental stresses. In this study, we report the characterization of a novel halotolerant PGPR strain (named C2) identified in a screen of rhizospheric bacterial isolates from southeast of Tunisia. Phylogenetic analysis showed that strain C2 is most likely affiliated to the genus Siccibacter with Siccibacter turicensis as the closest species (98.19%). This strain was able to perform phosphate solubilization and production of indole acetic acid (IAA), siderophores, hydrogen cyanide (HCN), as well as different hydrolytic enzymes (proteases, amylases, cellulases, and lipases). The potential of strain C2 in enhancing salt stress tolerance of Hordeum vulgare was also investigated. Our greenhouse inoculation assays showed that strain C2 promotes barley growth in the presence of 400 mM NaCl by increasing biomass, root length, and chlorophyll contents. It has a positive effect on the photosynthetic efficiency, concomitantly with lower intercellular CO₂ contents, compared to non-inoculated plants. Moreover, barley inoculation with strain C2 under salt stress, resulted in higher accumulation of proline and soluble sugars and alleviate the oxidative stress by decreasing hydrogen peroxide and malondialdehyde contents. Remarkably, this positive effect corroborates with a significant activation in the expression of a subset of barley stress responsive genes, including HVA1, HvDREB1, HvWRKY38 and HvP5CS. In summary, Siccibacter sp. strain C2 is able to enhance barley salt stress tolerance and should be leveraged in developing sustainable practices for cereal crop production.

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.

In vitro assessment of two novel Cellulases from Trabulsiella odontotermitis for agricultural waste utilization

Background

The production of agricultural wastes still growing as a consequence of the population growing. However, the majority of these residues are under-utilized due their chemical composition, which is mainly composed by cellulose. Actually, the search of cellulases with high efficiency to degrade this carbohydrate remains as the challenge. In the present experiment, two genes encoding an endoglucanase (EC 3.2.1.4) and β-glucosidase (EC 3.2.1.21) were overexpressed in Escherichia coli and their recombinant enzymes (egl-FZYE and cel-FZYE, respectively) characterized. Those genes were found in Trabulsiella odontermitis which was isolated from the gut of termite Heterotermes sp. Additionally, the capability to release sugars from agricultural wastes was evaluated in both enzymes, alone and in combination.

Results

The results have shown that optimal pH was 6.0 and 6.5, reaching an activity of 1051.65 ± 47.78 and 607.80 ± 10.19 U/mg at 39 °C, for egl-FZYE and cel-FZYE, respectively. The Km and Vmax for egl-FZYE using CMC as substrate were 11.25 mg/mL and 3921.57 U/mg, respectively, whereas using Avicel were 15.39 mg/mL and 2314.81 U/mg, respectively. The Km and Vmax for cel-FZYE using Avicel as substrate were 11.49 mg/mL and 2105.26 U/mg, respectively, whereas using CMC the enzyme did not had activity. Both enzymes had effect on agricultural wastes, and their effect was improved when they were combined reaching an activity of 955.1 ± 116.1, 4016.8 ± 332 and 1124.2 ± 241 U/mg on corn stover, sorghum stover and pine sawdust, respectively.

Conclusions

Both enzymes were capable of degrading agricultural wastes, and their effectiveness was improved up to 60% of glucose released when combined. In summary, the results of the study demonstrate that the recombinant enzymes exhibit characteristics that indicate their value as potential feed additives and that the enzymes could be used to enhance the degradation of cellulose in the poor-quality forage generally used in ruminant feedstuffs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-021-00687-6.

An overview on bioethanol production from lignocellulosic feedstocks

Lignocellulosic ethanol has been proposed as a green alternative to fossil fuels for many decades. However, commercialization of lignocellulosic ethanol faces major hurdles including pretreatment, efficient sugar release and fermentation. Several processes were developed to overcome these challenges e.g. simultaneous saccharification and fermentation (SSF). This review highlights the various ethanol production processes with their advantages and shortcomings. Recent technologies such as singlepot biorefineries, combined bioprocessing, and bioenergy systems with carbon capture are promising. However, these technologies have a lower technology readiness level (TRL), implying that additional efforts are necessary before being evaluated for commercial availability. Solving energy needs is not only a technological solution and interlinkage of various factors needs to be assessed beyond technology development.

Enzymatic hydrolysis of cellulose using extracts from insects

The use of Zophobas morio extracts in the aspect of cellulose hydrolysis is presented for the first time. The aim of this study was to investigate the action of enzymes obtained from Z. morio on cellulose hydrolysis and to determine their influence on the structural properties of cellulose with use the Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Cellulose hydrolysis products were analyzed by high performance liquid chromatography (HPLC). This analysis indicated that microcrystalline cellulose with smaller particle size was more susceptible to enzymatically treatment. Moreover, our investigation of cellulase activity showed a different profile of the used enzyme during particular developmental stages of Z. morio. Midgut extracts obtained from adult insects are more effective in degrading cellulose than extracts from larvae. The analysis of cellulose hydrolysis confirms that the efficiency of this reaction also depends on the structure of cellulosic materials and internal conditions of enzymatic reaction. In this study the cellulolytic activity of Z. morio midgut extracts showed that these insects could be valuable sources of cellulases.

RNA interference of endoglucanases in the formosan subterranean termite Coptotermes formosanus shiraki (Blattodea: Rhinotermitidae) by dsRNA injection or ingestion

Termites obtain energy and nutrition from wood and wood-related materials by utilizing endogenous and symbiotic cellulases. Endoglucanase is one of the key cellulases in cellulose digestion. Previous studies have shown that the inhibition of the cellulase enzyme system would be a plausible approach for termite control. In the present study, we studied the effect of RNAi on termites by targeting a conserved region of five endoglucanase genes from Coptotermes formosanus (CfEGs). Both dsRNA injection and oral delivery resulted in significant gene silencing of CfEGs and consequently led to mortality, reduced enzyme activity, and reduced weight compared to control worker termites. An injection dose of 150 ng and a feeding dose of 2 μg/cm² provided for the best RNAi efficiency. dsCfEG was further combined with flufenoxuron, an insect growth regulator used to manage/suppress subterranean termites, and when fed to workers, caused a lower enzyme activity compared to the dsCfEG- or flufenoxuron-only treatment. The weight loss (∼0.598 mg) and mortality (∼28%) observed in the combined dsCfEG and flufenoxuron treatment differed significantly from those observed in the flufenoxuron-only treatment (∼0.208 mg and ∼16%, respectively). Although the effects of these dsCfEG treatments on mortality were insufficient to serve as termiticides, dsCfEGs could be used in combination with other treatments to increase efficacy. This study provides a research basis for the use of RNAi in termiticides.

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.

Heterologous expression and biochemical characterization of a GHF9 endoglucanase from the termite Reticulitermes speratus in Pichia pastoris

BACKGROUND

Cellulases are of great significance for full utilization of lignocellulosic biomass. Termites have an efficient ability to degrade cellulose. Heterologous production of the termite-origin cellulases is the first step to realize their industrial applications. The use of P. pastoris for the expression of recombinant proteins has become popular. The endoglucanase from Reticulitermes speratus (RsEG), belonging to glycoside hydrolase family 9 (GHF9), has not been produced in P. pastoris yet.

RESULTS

A mutant RsEGm (G91A/Y97W/K429A) was successfully overexpressed in P. pastoris. RsEGm, with optimum pH 5.0, was active over the pH range of 4.0 to 9.0, and exhibited superior pH stability over between pH 4.0 and pH 11.0. It displayed the highest activity and good stability at 40 °C, but lost activity quickly at 50 °C. The apparent kinetic parameters of RsEGm against Carboxymethyl Cellulose (CMC) were determined, with K m and V max of 7.6 mg/ml and 5.4 μmol/min•mg respectively. Co2+, Mn2+ and Fe2+ enhanced the activity of RsEGm by 32.0, 19.5 and 11.2% respectively, while Pb2+ and Cu2+ decreased its activity by 19.6 and 12.7% separately.

CONCLUSIONS

RsEGm could be overexpressed in P. pastoris. It was stable between pH 4.0 and pH 11.0, and exhibited higher stability at temperatures ≤ 40 °C. This endoglucanase may have potential to be used in the field of laundry, textile and lignocellulose-based biofuels and chemicals.

Cross-reaction between Formosan termite (Coptotermes formosanus) proteins and cockroach allergens

Cockroach allergens can lead to serious allergy and asthma symptoms. Termites are evolutionarily related to cockroaches, cohabitate in human dwellings, and represent an increasing pest problem in the United States. The Formosan subterranean termite (Coptotermes formosanus) is one of the most common species in the southern United States. Several assays were used to determine if C. formosanus termite proteins cross-react with cockroach allergens. Expressed sequence tag and genomic sequencing results were searched for homology to cockroach allergens using BLAST 2.2.21 software. Whole termite extracts were analyzed by mass-spectrometry, immunoassay with IgG and scFv antibodies to cockroach allergens, and human IgE from serum samples of cockroach allergic patients. Expressed sequence tag and genomic sequencing results indicate greater than 60% similarity between predicted termite proteins and German and American cockroach allergens, including Bla g 2/Per a 2, Bla g 3/Per a 3, Bla g 5, Bla g 6/Per a 6, Bla g 7/Per a 7, Bla g 8, Per a 9, and Per a 10. Peptides from whole termite extract were matched to those of the tropomyosin (Bla g 7), arginine kinase (Per a 9), and myosin (Bla g 8) cockroach allergens by mass-spectrometry. Immunoblot and ELISA testing revealed cross-reaction between several proteins with IgG and IgE antibodies to cockroach allergens. Several termite proteins, including the hemocyanin and tropomyosin orthologs of Blag 3 and Bla g 7, were shown to crossreact with cockroach allergens. This work presents support for the hypothesis that termite proteins may act as allergens and the findings could be applied to future allergen characterization, epitope analysis, and clinical studies.

Transcription Analysis of the Beta-Glucosidase Precursor in Wild-Type and l-4i Mutant Bombyx mori (Lepidoptera: Bombycidae)

Lethal fourth-instar larvae (l-4i) mutant of Bombyx mori, a recently discovered novel mutant, die from energy depletion due to genetic mutation. Beta-glucosidase is a common digestive enzyme that hydrolyzes cellulose in the diet to provide energy. In this study, the mRNA expression profiles of B. mori beta-glucosidase precursor (BmpreBG) were characterized by reverse transcription polymerase chain reaction and quantitative real-time polymerase chain reaction. The transcription level of BmpreBG varied in different tissues and developmental stages, except in the pupa and moth, which are the no-diet period. Remarkably, the mRNA expression level of BmpreBG was sharply reduced in l-4i but not in the wild type, which suggested that the digestive function of the mutant was severely damaged. This was consistent with the l-4i phenotypic traits of not eating mulberries, lack of energy, and ultimate death. 5'-rapid amplification of cDNA ends showed, for the first time, that BmpreBG has a 160-bp 5'-untranslated region. These findings suggested that B. mori β-glucosidase precursor was involved in the death process of l-4i mutant larvae.

Characterization of Cryptopygus antarcticus endo-β-1,4-glucanase from Bombyx mori expression systems

Endo-β-1,4-glucanase (CaCel) from Antarctic springtail, Cryptopygus antarcticus, a cellulase with high activity at low temperature, shows potential industrial use. To obtain sufficient active cellulase for characterization, CaCel gene was expressed in Bombyx mori-baculovirus expression systems. Recombinant CaCel (rCaCel) has been expressed in Escherichia coli (Ec-CaCel) at temperatures below 10°C, but the expression yield was low. Here, rCaCel with a silkworm secretion signal (Bm-CaCel) was successfully expressed and secreted into pupal hemolymph and purified to near 90% purity by Ni-affinity chromatography. The yield and specific activity of rCaCel purified from B. mori were estimated at 31 mg/l and 43.2 U/mg, respectively, which is significantly higher than the CaCel yield obtained from E. coli (0.46 mg/l and 35.8 U/mg). The optimal pH and temperature for the rCaCels purified from E. coli and B. mori were 3.5 and 50°C. Both rCaCels were active at a broad range of pH values and temperatures, and retained more than 30% of their maximal activity at 0°C. Oligosaccharide structural analysis revealed that Bm-CaCel contains elaborated N- and O-linked glycans, whereas Ec-CaCel contains putative O-linked glycans. Thermostability of Bm-CaCel from B. mori at 60°C was higher than that from E. coli, probably due to glycosylation.

Expression of the Thermobifida fusca xylanase Xyn11A in Pichia pastoris and its characterization

BACKGROUND

Xylan is a major component of plant cells and the most abundant hemicellulose. Xylanases degrade xylan into monomers by randomly cleaving β-1,4-glycosidic bonds in the xylan backbone, and have widespread potential applications in various industries. The purpose of our study was to clone and express the endoxylanase gene xynA of Thermobifida fusca YX in its native form and with a C-terminal histidine (His) tag in Pichia pastoris X-33. We analyzed and compared these two forms of the protein and examined their potential applications in various industries.

RESULTS

The xynA gene from T. fusca YX was successfully cloned and expressed using P. pastoris X-33. We produced a recombinant native form of the protein (rXyn11A) and a C-terminal His-tagged form of the desired protein (rXyn11A-(His)6). The specific activities of rXyn11A and rXyn11A-(His)6 in culture supernatants approached 149.4 and 133.4 U/mg, respectively. These activities were approximately 4- and 3.5-fold higher than those for the non-recombinant wild-type Xyn11A (29.3 U/mg). Following purification, the specific activities of rXyn11A and rXyn11A-(His)6 were 557.35 and 515.84 U/mg, respectively. The specific activity of rXyn11A was 8% higher than that of rXyn11A-(His)6. Both recombinant xylanases were optimally active at 80°C and pH 8.0, and exhibited greater than 60% activity between pH 6-9 and 60-80°C. They exhibited similar pH stability, while rXyn11A exhibited better thermostability; N-glycosylation enhanced the thermostability of both recombinant xylanases. The products of beechwood xylan hydrolyzed by both xylanases included xylobiose, xylotriose, xylotetraose and xylopentaose.

CONCLUSIONS

The C-terminal His tag had adverse effects when added to the Xyn11A protein. The thermostability of both recombinant xylanases was enhanced by N-glycosylation. Their stabilities at a high pH and temperature indicate their potential for application in various industries.

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.

Expression of an endoglucanase from Tribolium castaneum (TcEG1) in Saccharomyces cerevisiae

Insects are a largely unexploited resource in prospecting for novel cellulolytic enzymes to improve the production of ethanol fuel from lignocellulosic biomass. The cost of lignocellulosic ethanol production is expected to decrease by the combination of cellulose degradation (saccharification) and fermentation of the resulting glucose to ethanol in a single process, catalyzed by the yeast Saccharomyces cerevisiae transformed to express efficient cellulases. While S. cerevisiae is an established heterologous expression system, there are no available data on the functional expression of insect cellulolytic enzymes for this species. To address this knowledge gap, S. cerevisiae was transformed to express the full-length cDNA encoding an endoglucanase from the red flour beetle, Tribolium castaneum (TcEG1), and evaluated the activity of the transgenic product (rTcEG1). Expression of the TcEG1 cDNA in S. cerevisiae was under control of the strong glyceraldehyde-3 phosphate dehydrogenase promoter. Cultured transformed yeast secreted rTcEG1 protein as a functional β-1,4-endoglucanase, which allowed transformants to survive on selective media containing cellulose as the only available carbon source. Evaluation of substrate specificity for secreted rTcEG1 demonstrated endoglucanase activity, although some activity was also detected against complex cellulose substrates. Potentially relevant to uses in biofuel production rTcEG1 activity increased with pH conditions, with the highest activity detected at pH 12. Our results demonstrate the potential for functional production of an insect cellulase in S. cerevisiae and confirm the stability of rTcEG1 activity in strong alkaline environments.

cDNA cloning and heterologous expression of an endo-β-1,4-glucanase from the fungus-growing termite Macrotermes barneyi

Major β-glucosidase (BG) and endo-β-1,4-glucanase (EG) activities were localized to the midgut of the fungus-growing termite Macrotermes barneyi. Previously, we obtained the endogenous BG gene (MbmgBG1) from the midgut of M. barneyi. Here, we report the cDNA cloning of another endogenous cellulase, the EG protein MbEG1. This cellulase was partially purified from crude extract of the midgut of worker termites using zymogram analysis. Based on the N-terminal amino acid sequence and using rapid amplification of cDNA ends (RACE), a full-length cDNA of 1,843 base pairs was obtained. This encoded 448 amino acids and the sequence was similar to that of the members of glycoside hydrolase family 9. The MbEG1 transcript was detected primarily in the midgut using quantitative real-time polymerase chain reaction (PCR). To confirm functional activity of MbEG1, heterologous expression was conducted in both Escherichia coli and Pichia pastoris expression systems. Results indicated that MbEG1 could be functionally expressed in P. pastoris. This study provides the information that may facilitate understanding of cellulolytic systems in fungus-growing termites.

Gene expression and molecular phylogenetic analyses of beta-glucosidase in the termite Reticulitermes speratus (Isoptera: Rhinotermitidae)

Beta-glucosidase (BG) is known as a multifunctional enzyme for social maintenance in terms of both cellulose digestion and social communication in termites. However, the expression profiles of each BG gene and their evolutionary history are not well understood. First, we cloned two types of BG homologs (RsBGI and RsBGII) from the termite Reticulitermes speratus (Kolbe). Gene expression analyses showed that RsBGI expression levels of primary queens and kings from 30 to 100 days after colony foundation were high, but those of reproductives dropped after day 400. Extremely low gene expression levels of RsBGI were observed in eggs, whereas workers had significantly higher expression levels than those of soldiers and other colony members. Consequently, RsBGI gene expression levels changed among each developmental stage, and RsBGI was shown to be involved in cellulose digestion. On the other hand, the RsBGII gene was consistently expressed in all castes and developmental stages examined, and notable expression changes were not observed among them, including in eggs. It was indicated that RsBGII is a main component involved in social communication, for example, the egg-recognition pheromone shown in this species previously. Finally, we obtained partial gene homologs from other termite and cockroach species, including the woodroach (genus Cryptocercus), which is the sister group to termites, and performed molecular phylogenetic analyses. The results showed that the origin of the BG gene homologs preceded the divergence of termites and cockroaches, suggesting that the acquisition of multifunctionality of the BG gene also occurred in cockroach lineages.

Deciphering the synergism of endogenous glycoside hydrolase families 1 and 9 from Coptotermes gestroi

Termites can degrade up to 90% of the lignocellulose they ingest using a repertoire of endogenous and symbiotic degrading enzymes. Termites have been shown to secrete two main glycoside hydrolases, which are GH1 (EC 3.2.1.21) and GH9 (EC 3.2.1.4) members. However, the molecular mechanism for lignocellulose degradation by these enzymes remains poorly understood. The present study was conducted to understand the synergistic relationship between GH9 (CgEG1) and GH1 (CgBG1) from Coptotermes gestroi, which is considered the major urban pest of São Paulo State in Brazil. The goal of this work was to decipher the mode of operation of CgEG1 and CgBG1 through a comprehensive biochemical analysis and molecular docking studies. There was outstanding degree of synergy in degrading glucose polymers for the production of glucose as a result of the endo-β-1,4-glucosidase and exo-β-1,4-glucosidase degradation capability of CgEG1 in concert with the high catalytic performance of CgBG1, which rapidly converts the oligomers into glucose. Our data not only provide an increased comprehension regarding the synergistic mechanism of these two enzymes for cellulose saccharification but also give insight about the role of these two enzymes in termite biology, which can provide the foundation for the development of a number of important applied research topics, such as the control of termites as pests as well as the development of technologies for lignocellulose-to-bioproduct applications.

The cellulolytic system of the termite gut

The demand for the usage of natural renewable polymeric material is increasing in order to satisfy the future needs for energy and chemical precursors. Important steps in the hydrolysis of polymeric material and bioconversion can be performed by microorganisms. Over about 150 million years, termites have optimized their intestinal polysaccharide-degrading symbiosis. In the ecosystem of the "termite gut," polysaccharides are degraded from lignocellulose, such as cellulose and hemicelluloses, in 1 day, while lignin is only weakly attacked. The understanding of the principles of cellulose degradation in this natural polymer-degrading ecosystem could be helpful for the improvement of the biotechnological hydrolysis and conversion of cellulose, e.g., in the case of biogas production from natural renewable plant material in biogas plants. This review focuses on the present knowledge of the cellulose degradation in the termite gut.

Defining host-symbiont collaboration in termite lignocellulose digestion: "The view from the tip of the iceberg"

Termites have the unique ability to exploit lignocellulose as a primary nutrition source. Traditionally, termite lignocellulose digestion has been considered as a gut-symbiont-mediated process; however, in recent years the importance of host digestive capabilities have become apparent. Despite this growing understanding, how digestive enzymes from different origins specifically collaborate (i.e., additively or synergistically) has remained largely unknown. In a recent study, we undertook translational-genomic studies to address these questions in the lower termite Reticulitermes flavipes (Isoptera: Rhinotermitidae) and its symbiotic gut fauna. We used a combination of native gut tissue preparations and recombinant enzymes derived from the host gut transcriptome to identify synergistic collaborations between host and symbiont, and also among enzymes produced exclusively by the host termite. These findings provided important new evidence of synergistic collaboration among enzymes in the release of fermentable monosaccharides from wood lignocellulose, and laid a foundation for future integrative studies into termite digestion, symbiosis and eusociality.

Carbohydrate-active enzymes revealed in Coptotermes formosanus (Isoptera: Rhinotermitidae) transcriptome

Coptotermes formosanus is one of the most destructive wood-feeding termites. To understand the molecular mechanisms that regulate the development of the termite, a normalized C. formosanus cDNA library was constructed using mixed RNA isolated from workers, soldiers, nymphs and alates of both sexes. The sequencing of this library generated 131 636 expressed sequence tags (ESTs) and 25 939 assembled unigenes. The carbohydrate-active enzymes (CAZymes) revealed in this library were analysed in the present report. A total of 509 putative CAZymes were identified. Diverse cellulolytic enzymes were uncovered from both the host termite and from symbionts harboured by the termite, which were possibly the result of the high efficiency of cellulose utilization. CAZymes associated with trehalose biosynthetic and metabolic pathways were also identified, which are potential regulators of the physiological activities of trehalose, an important insect blood sugar. Representative CAZyme coding genes in glycoside hydrolase family 1 (GH1) were quantitatively analysed. The results showed that the five GH1 β-glucosidase genes were expressed differentially among different castes and one of them was female alate-specific. Overall, the normalized EST library provides a comprehensive genetic resource of C. formosanus and will serve a diverse range of research areas. The CAZymes represent one of the repositories of enzymes useful for physiological studies and applications in sugar-based biofuel production.

Functional analyses of the digestive β-glucosidase of Formosan subterranean termites (Coptotermes formosanus)

The research was to elucidate the function of the β-glucosidase of Formosan subterranean termites in vitro and in vivo. The gene transcript was detected predominantly in the salivary gland tissue, relative to the midgut and the hindgut of the foraging worker caste, indicating salivary glands were the major expression sites of the β-glucosidase. Using recombinant β-glucosidase produced in Escherichia coli, the enzyme showed higher affinity and activity toward cellobiose and cellotriose than other substrates tested. In assessing impacts of specific inhibitors, we found that the β-glucosidase could be irreversibly inactivated by conduritol B epoxide (CBE) but not gluconolactone. Termite feeding assays showed that the CBE treatment reduced the glucose supply in the midgut and resulted in the body weight loss while no effect was observed for the gluconolactone treatment. These findings highlighted that the β-glucosidase is one of the critical cellulases responsible for cellulose degradation and glucose production; inactivation of these digestive enzymes by specific inhibitors may starve the termite.

Functional characterization and target discovery of glycoside hydrolases from the digestome of the lower termite Coptotermes gestroi

BACKGROUND

Lignocellulosic materials have been moved towards the forefront of the biofuel industry as a sustainable resource. However, saccharification and the production of bioproducts derived from plant cell wall biomass are complex and lengthy processes. The understanding of termite gut biology and feeding strategies may improve the current state of biomass conversion technology and bioproduct production.

RESULTS

The study herein shows comprehensive functional characterization of crude body extracts from Coptotermes gestroi along with global proteomic analysis of the termite's digestome, targeting the identification of glycoside hydrolases and accessory proteins responsible for plant biomass conversion. The crude protein extract from C. gestroi was enzymatically efficient over a broad pH range on a series of natural polysaccharides, formed by glucose-, xylose-, mannan- and/or arabinose-containing polymers, linked by various types of glycosidic bonds, as well as ramification types. Our proteomic approach successfully identified a large number of relevant polypeptides in the C. gestroi digestome. A total of 55 different proteins were identified and classified into 29 CAZy families. Based on the total number of peptides identified, the majority of components found in the C. gestroi digestome were cellulose-degrading enzymes. Xylanolytic enzymes, mannan- hydrolytic enzymes, pectinases and starch-degrading and debranching enzymes were also identified. Our strategy enabled validation of liquid chromatography with tandem mass spectrometry recognized proteins, by enzymatic functional assays and by following the degradation products of specific 8-amino-1,3,6-pyrenetrisulfonic acid labeled oligosaccharides through capillary zone electrophoresis.

CONCLUSIONS

Here we describe the first global study on the enzymatic repertoire involved in plant polysaccharide degradation by the lower termite C. gestroi. The biochemical characterization of whole body termite extracts evidenced their ability to cleave all types of glycosidic bonds present in plant polysaccharides. The comprehensive proteomic analysis, revealed a complete collection of hydrolytic enzymes including cellulases (GH1, GH3, GH5, GH7, GH9 and CBM 6), hemicellulases (GH2, GH10, GH11, GH16, GH43 and CBM 27) and pectinases (GH28 and GH29).

High throughput screening of hydrolytic enzymes from termites using a natural substrate derived from sugarcane bagasse

BACKGROUND

The description of new hydrolytic enzymes is an important step in the development of techniques which use lignocellulosic materials as a starting point for fuel production. Sugarcane bagasse, which is subjected to pre-treatment, hydrolysis and fermentation for the production of ethanol in several test refineries, is the most promising source of raw material for the production of second generation renewable fuels in Brazil. One problem when screening hydrolytic activities is that the activity against commercial substrates, such as carboxymethylcellulose, does not always correspond to the activity against the natural lignocellulosic material. Besides that, the macroscopic characteristics of the raw material, such as insolubility and heterogeneity, hinder its use for high throughput screenings.

RESULTS

In this paper, we present the preparation of a colloidal suspension of particles obtained from sugarcane bagasse, with minimal chemical change in the lignocellulosic material, and demonstrate its use for high throughput assays of hydrolases using Brazilian termites as the screened organisms.

CONCLUSIONS

Important differences between the use of the natural substrate and commercial cellulase substrates, such as carboxymethylcellulose or crystalline cellulose, were observed. This suggests that wood feeding termites, in contrast to litter feeding termites, might not be the best source for enzymes that degrade sugarcane biomass.

Characterization of a new endogenous endo-β-1,4-glucanase of Formosan subterranean termite (Coptotermes formosanus)

The present work characterized a new endogenous cellulase (endo-β-1,4-glucanase) gene, CfEG5, uncovered in the transcriptome of Formosan subterranean termite (Coptotermes formosanus). The full-length gene was cloned and sequenced. It is similar to the CfEG3a described earlier (Zhang et al., 2009) but not likely an allelic variant. GenomeWalker™ DNA walking analysis indicated that there may be one copy of CfEG5 and two copies of CfEG3a in the termite genome. As with CfEG3a, the transcript of CfEG5 was detected predominantly in the salivary gland based on quantitative RT-PCR. Phylogenetic analysis of translated amino acid sequence showed that the CfEG5 is more related to CaEG, derived from an Australian subterranean termite (Coptotermes acinaciformis), than CfEG3a and other cellulases from Coptotermes formosanus, Reticulitermes speratus, or Reticulitermes flavipes. Recombinant CfEG5, produced in Escherichia coli, was active against filter-paper cellulose, resulting in mostly cellobiose and cellotriose, similar to the enzymatic and biochemical properties of CfEG3a. These findings would lead to further investigation of both the evolutionary origin of eukaryotic cellulase genes and the evolutionary relationship of termite species. The cellulose-degrading enzyme is applicable for bioconversion of wood to simple sugars and production of biofuels. The recombinant cellulase should also be useful for designing and screening of inhibitors for the development of target-specific and environment-friendly bio-termicides.

Identification, cloning, and expression of a GHF9 cellulase from Tribolium castaneum (Coleoptera: Tenebrionidae)

The availability of sequenced insect genomes has allowed for discovery and functional characterization of novel genes and proteins. We report use of the Tribolium castaneum (Herbst) (red flour beetle) genome to identify, clone, express, and characterize a novel endo-β-1,4-glucanase we named TcEG1 (T. castaneum endoglucanase 1). Sequence analysis of a full-length TcEG1 cDNA clone (1356bp) revealed sequence homology to enzymes in glycosyl hydrolase family 9 (GHF9), and verified presence of a change (Gly for Ser) in the conserved catalytic domain for GHF9 cellulases. This TcEG1 cDNA clone was predicted to encode a 49.5kDa protein with a calculated pI of 5.39. Heterologous expression of TcEG1 in Drosophila S2 cell cultures resulted in secretion of a 51-kDa protein, as determined by Western blotting. The expressed protein was used to characterize TcEG1 enzymatic activity against two cellulose substrates to determine its specificity and stability. Our data support that TcEG1 as a novel endo-β-1,4-glucanase, the first functional characterization of a cellulase enzyme derived from an insect genome with potential applications in the biofuel industry due to its high relative activity at alkaline pH.

Characterization of a new β-glucosidase/β-xylosidase from the gut microbiota of the termite (Reticulitermes santonensis)

The gut of the termite Reticulitermes santonensis contains an interesting diversity of prokaryotic and eukaryotic microorganisms not found elsewhere. These microorganisms produce many enzyme-digesting lignocellulosic compounds, probably in cooperation with endogenous enzymes. Regarding cellulose and hemicellulose digestion in the termite gut, much remains to be learned about the relative contributions of termite enzymes and enzymes produced by different microorganisms. Here we grew bacterial colonies from termite gut suspensions, identifying 11 of them after PCR amplification of their 16S rRNA genes. After constructing in Escherichia coli a genomic DNA library corresponding to all of the colonies obtained, we performed functional screening for α-amylase, xylanase, β-glucosidase, and endoglucanase activities. This screen revealed a clone producing β-glucosidase activity. Sequence analysis showed that the cloned genomic DNA fragment contained three complete ORFs (bglG, bglF, and bglB) organized in a putative bgl operon. The new β-glucosidase (BglB), identified with its regulators BglG and BglF, belongs to glycoside hydrolase family 1. The new β-glucosidase was expressed in E. coli and purified by affinity chromatography. The purified enzyme shows maximal activity at pH 6.0 and 40 °C. It also displays β-xylosidase activity.

Production and characterization of a recombinant beta-1,4-endoglucanase (glycohydrolase family 9) from the termite Reticulitermes flavipes

Cell-1 is a host-derived beta-1,4-endoglucanase (Glycohydrolase Family 9 [GHF9]) from the lower termite Reticulitermes flavipes. Here, we report on the heterologous production of Cell-1 using eukaryotic (Baculovirus Expression Vector System; BEVS) and prokaryotic (E. coli) expression systems. The BEVS-expressed enzyme was more readily obtained in solubilized form and more active than the E. coli-expressed enzyme. K(m) and V(max) values for BEVS-expressed Cell-1 against the model substrate CMC were 0.993% w/v and 1.056 micromol/min/mg. Additional characterization studies on the BEVS-expressed enzyme revealed that it possesses activity comparable to the native enzyme, is optimally active around pH 6.5-7.5 and 50-60 degrees C, is inhibited by EDTA, and displays enhanced activity up to 70 degrees C in the presence of CaCl(2). These findings provide a foundation on which to begin subsequent investigations of collaborative digestion by coevolved host and symbiont digestive enzymes from R. flavipes that include GHF7 exoglucanases, GHF1 beta glucosidases, phenol-oxidizing laccases, and others.

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

BACKGROUND

Termite lignocellulose digestion is achieved through a collaboration of host plus prokaryotic and eukaryotic symbionts. In the present work, we took a combined host and symbiont metatranscriptomic approach for investigating the digestive contributions of host and symbiont in the lower termite Reticulitermes flavipes. Our approach consisted of parallel high-throughput sequencing from (i) a host gut cDNA library and (ii) a hindgut symbiont cDNA library. Subsequently, we undertook functional analyses of newly identified phenoloxidases with potential importance as pretreatment enzymes in industrial lignocellulose processing.

RESULTS

Over 10,000 expressed sequence tags (ESTs) were sequenced from the 2 libraries that aligned into 6,555 putative transcripts, including 171 putative lignocellulase genes. Sequence analyses provided insights in two areas. First, a non-overlapping complement of host and symbiont (prokaryotic plus protist) glycohydrolase gene families known to participate in cellulose, hemicellulose, alpha carbohydrate, and chitin degradation were identified. Of these, cellulases are contributed by host plus symbiont genomes, whereas hemicellulases are contributed exclusively by symbiont genomes. Second, a diverse complement of previously unknown genes that encode proteins with homology to lignase, antioxidant, and detoxification enzymes were identified exclusively from the host library (laccase, catalase, peroxidase, superoxide dismutase, carboxylesterase, cytochrome P450). Subsequently, functional analyses of phenoloxidase activity provided results that were strongly consistent with patterns of laccase gene expression. In particular, phenoloxidase activity and laccase gene expression are mostly restricted to symbiont-free foregut plus salivary gland tissues, and phenoloxidase activity is inducible by lignin feeding.

CONCLUSION

To our knowledge, this is the first time that a dual host-symbiont transcriptome sequencing effort has been conducted in a single termite species. This sequence database represents an important new genomic resource for use in further studies of collaborative host-symbiont termite digestion, as well as development of coevolved host and symbiont-derived biocatalysts for use in industrial biomass-to-bioethanol applications. Additionally, this study demonstrates that: (i) phenoloxidase activities are prominent in the R. flavipes gut and are not symbiont derived, (ii) expands the known number of host and symbiont glycosyl hydrolase families in Reticulitermes, and (iii) supports previous models of lignin degradation and host-symbiont collaboration in cellulose/hemicellulose digestion in the termite gut. All sequences in this paper are available publicly with the accession numbers FL634956-FL640828 (Termite Gut library) and FL641015-FL645753 (Symbiont library).