Purification, characterization and sequencing of the major beta-1,3-glucanase from the midgut of Tenebrio molitor larvae

Identification and Characterization of Two Novel Extracellular β-Glucanases from Chaetomium globosum against Fusarium sporotrichioides

Chaetomium globosum can inhibit the growth of fusarium by means of their extracellular proteins. Two novel β-glucanases, designated Cgglu17A and Cgglu16B, were separated from the supernatant of C. globosum W7 and verified to have the ability to hydrolyze cell walls of Fusarium sporotrichioides MLS-19. Cgglu17A (397 amino acids) was classified as glycoside hydrolase family 17 while Cgglu16B belongs to the family16 (284 amino acids). Recombinant protein Cgglu17A was successfully expressed in Escherichia coli, and the enzymes were purified by affinity chromatography. Maximum activity of Cgglu17A appeared at the pH 5.5 and temperature 50 °C, but Cgglu16B shows the maximum activity at the pH 5.0 and temperature 50 °C. Most of heavy metal ions had inhibition effect on the two enzymes, but Cgglu17A and Cgglu16B were respectively activated by Ba2+ and Mn2+. Cgglu17A exhibited high substrate specificity, almost only catalyzing the cleavage of β-1,3-glycosidic bond, in various polysaccharose, to liberate glucose. However, Cgglu16B showed high catalytic activities to both β-1,3-glycosidic and β-1,3-1,4-glycosidic bonds. Cgglu17A was an exo-glucanase, but Cgglu16B was an endo-glucanase based on hydrolytic properties assay. Both of two enzymes showed potential antifungal activity, and the synergistic effect was observed in the germination experiment of pathogenic fungus. In conclusion, Cgglu17A (exo-1,3-β-glucanase) and Cgglu16B (endo-1,3(4)-β-glucanase) were confirmed to play a key role in the process of C. globosum controlling fusarium and have potential application value on industry and agriculture for the first time.

Effects of Yellow Mealworm (Tenebrio molitor) on Growth Performance, Hepatic Health and Digestibility in Juvenile Largemouth Bass (Micropterus salmoides)

This study investigated the effects of yellow mealworm meal (TM) on growth performance, hepatic health and digestibility in juvenile largemouth bass (Micropterus salmoides). The fish were fed with the basic feed and the test feed (70% basic feed and 30% raw materials) containing Cr₂O₃, and feces were collected for digestibility determination. The fish were fed with five isonitrogenous (47% crude protein) and isolipidic (13% crude lipid) diets, in which fishmeal (FM) was replaced with 0% (TM0), 12% (TM12), 24% (TM24), 36% (TM36) and 48% (TM48) TM. The fish were reared in cylindrical plastic tanks in a recirculating aquaculture system for 11 weeks. The apparent digestibility coefficients (ADC), of dry matter, crude protein and crude lipid, in largemouth bass of TM were 74.66%, 91.03% and 90.91%, respectively. The ADC of total amino acid (TAA) of TM in largemouth bass was 92.89%, and the ADC of essential amino acid (EAA) in TM in largemouth bass was 93.86%. The final body weight (FBW), weight gain rate (WGR) and specific growth rate (SGR) in the TM24 group were significantly higher than those in other groups. Similarly, the highest mRNA expression levels of hepatic protein metabolism genes (pi3k, mtor, 4ebp2 and got) and antioxidant enzyme (glutathione peroxidase, Gpx; catalase, Cat) activities were observed in the TM24 group. Moreover, the expression levels of anti-inflammatory factors (il-10 and tgf) in liver were up-regulated and the expression levels of pro-inflammatory factors (il-8 and il-1β) in liver were down-regulated. Quadratic regression model analysis, based on weight gain rate (WGR) against dietary TM level, indicated that the optimum level of dietary TM replacing FM in largemouth bass diet was 19.52%. Appropriate replacement levels (less than 36%) of FM by TM in the diets can enhance the antioxidant capacity and immunity of largemouth bass. However, high levels of FM substitution with TM (more than 48%) in the feeds can damage the liver health and inhibit the growth of largemouth bass. Notably, largemouth bass has high ADC and high utilization of TM, which indicates that it is feasible to use TM as feed protein source for largemouth bass.

Characterization of two 1,3-β-glucan-modifying enzymes from Penicillium sumatraense reveals new insights into 1,3-β-glucan metabolism of fungal saprotrophs

BACKGROUND

1,3-β-glucan is a polysaccharide widely distributed in the cell wall of several phylogenetically distant organisms, such as bacteria, fungi, plants and microalgae. The presence of highly active 1,3-β-glucanases in fungi evokes the biological question on how these organisms can efficiently metabolize exogenous sources of 1,3-β-glucan without incurring in autolysis.

RESULTS

To elucidate the molecular mechanisms at the basis of 1,3-β-glucan metabolism in fungal saprotrophs, the putative exo-1,3-β-glucanase G9376 and a truncated form of the putative glucan endo-1,3-β-glucosidase (ΔG7048) from Penicillium sumatraense AQ67100 were heterologously expressed in Pichia pastoris and characterized both in terms of activity and structure. G9376 efficiently converted laminarin and 1,3-β-glucan oligomers into glucose by acting as an exo-glycosidase, whereas G7048 displayed a 1,3-β-transglucanase/branching activity toward 1,3-β-glucan oligomers with a degree of polymerization higher than 5, making these oligomers more recalcitrant to the hydrolysis acted by exo-1,3-β-glucanase G9376. The X-ray crystallographic structure of the catalytic domain of G7048, solved at 1.9 Å of resolution, consists of a (β/α)₈ TIM-barrel fold characteristic of all the GH17 family members. The catalytic site is in a V-shaped cleft containing the two conserved catalytic glutamic residues. Molecular features compatible with the activity of G7048 as 1,3-β-transglucanase are discussed.

CONCLUSIONS

The antagonizing activity between ΔG7048 and G9376 indicates how opportunistic fungi belonging to Penicillium genus can feed on substrates similar for composition and structure to their own cell wall without incurring in a self-deleterious autohydrolysis.

Cloning and Functional Characterization of a Novel β-GRP Gene From Melanotus cribricollis

In this study, a novel β-1,3-glucan recognition protein gene (β-GRP) was identified from Melanotus cribricollis, and its potential role in the immune response was investigated. The full length of β-GRP cDNA (Accession Number: MT941530) was 1644 bp, encoding a protein composed of 428 amino acids. The theoretical molecular weight and the isoelectric point were 51.53 kDa and 6.17, respectively. The amino acid sequence of β-GRP from M. cribricollis was closely related to that of. β-GRP-like from Photinus pyralis, and was predicted to contain conserved GH16 domain without glucanase active site. The results of real-time quantitative PCR showed that fungal infection of Metarhizium pingshaense may significantly upregulated the expression level of β-GRP gene. The RNAi suppression of β-GRP gene expression significantly increased the corrected cumulative mortality. Meanwhile, antimicrobial peptide genes defensin and lysozyme were significantly downregulated after interference of β-GRP. Taken together, these results suggest that β-GRP of M. cribricollis probably participates in the host immune system by mediating the expression of antimicrobial peptides. This study provides comprehensive insights into the innate immune system of insect larvae.

Heterologous expression and characterization of a novel glycoside hydrolase family 55 β-1,3-glucanase, AcGluA, from Archangium sp. strain AC19

Some microbial-associated molecular patterns (MAMPs), like glucan oligosaccharides, can be recognized by pattern recognition receptors (PRRs) of plant to elicit further immunity response. In this study, a novel glycoside hydrolase family 55 β-1,3-glucanase (AcGluA) from Archangium sp. strain AC19 was cloned and expressed in Escherichia coli. Among the reported β-1, 3-glucanases from the glycoside hydrolase 55 family, the purified AcGluA exhibited the highest activity on laminarin at pH 6.0 and 60 °C with 112.3 U/mg. Activity of AcGluA was stable in the range of pH 4.0-9.0 and at temperatures below 60 °C. The K_m and V_max of AcGluA for laminarin were 3.5 mg/ml and 263.5 μmol/(ml·min). AcGluA hydrolyzed laminarin into a series of oligosaccharides, suggesting it was an endo-β-1,3-glucanase. The high dose of oligosaccharides (1600 mg/l) had conspicuous biocontrol efficacy on the defense of rice seedlings to Magnaporthe oryzae, which provided a new idea for the development of green biopesticide.Key points• The AcGluA was determined bacteria-derived β-1,3-glucanases in the GH55 family.• The AcGluA showed the highest activity towards laminarin among reported GH55 family.• The hydrolysates of laminarin showed conspicuous biocontrol efficacy to M. oryzae.

Beta-1,3-glucanase inhibitors in Brazilian brown seaweed

Beta-1,3-glucanases are enzymes that hydrolyze beta-1,3-glucans, and they are essential for the metabolism of seaweed, plants and fungi. These enzymes also participate in the digestion of herbivore and fungivore animals. Because of the importance of these enzymes in insects, beta-1,3-glucanase inhibitors may be used for the development of new control strategies against agricultural pests and disease vectors. Beta-1,3-glucanase inhibitors have been described in the brown seaweed Laminaria cichorioides, but were never recorded in Brazilian seaweed species. We evaluated the presence of beta-1,3-glucanase inhibitors in samples of Padina gymnospora, Dictyota sp., Colpomenia sinuosa, and Lobophora sp., collected in Arraial d'Ajuda (Bahia). Ethanolic or buffer extracts were used in inhibition tests against the beta-1,3-glucanase of Trichoderma sp. Extracts in buffer showed no inhibition, but ethanolic extracts from all species showed different extents of inhibition. Samples from Dictyota sp. and P. gymnospora showed inhibitions above 75% (absolute ethanol) or 50% (ethanol 50%). In summary, extraction with absolute ethanol resulted in better inhibitions, and P. gymnospora showed the higher inhibitions. Brazilian seaweed may be good sources of beta-1,3-glucanase inhibitors for biochemical and physiological studies of these enzymes. Besides that, these molecules show potential for the development of new biotechnological tools for insect control.

Cloning, expression, and functional analysis of the β-1,3-glucanase gene in Ostrinia furnacalis

The β-1,3-glucanase gene in Ostrinia furnacalis was first obtained by RT-PCR. The real-time fluorescence quantitative PCR showed that the expression level of β-1,3-glucanase in the midgut of O. furnacalis was higher than in other tissues. Moreover, the expression level in the larval stage was higher in egg, pupa, and adult stages. The optimal pH of recombinant O. furnacalis β-1,3-glucanase OfLam to the substrate laminarin was 4.5, and the optimum reaction temperature was 50°C. The enzyme exhibited a K_M of 1.59 ± 0.28 mg/mL and a k_cat of 15.8 ± 0.66 s^-1 . Ostrinia furnacalis β-1,3-glucanase has a similar catalytic efficiency to other insect-derived β-1,3-glucanases. The recombinant OfLam has a broad substrate spectrum and can hydrolyze fungal cell walls, suggesting a new source of enzymes for biological control strategies that target fungal cell walls.

Laminarans and 1,3-β-D-glucanases

The laminarans are biologically active water-soluble polysaccharide (1,3;1,6-β-D-glucans) of brown algae. These polysaccharides are an attractive object for research due to its relatively simple structure, low toxicity, and various biological effects. 1,3-β-D-glucanases are an effective tool for studying the structure of laminarans, and can also be used to obtain new biologically active derivatives. This review is to outline what is currently known about laminarans and enzymes that catalyze of their transformation. We focused on information about sources, structure and properties of laminarans and 1,3-β-D-glucanases, methods of obtaining and structural elucidation of laminarans, and biological activity of laminarans and products of their enzymatic transformation. It has an increased focus on the immunomodulating and anticancer activity of laminarans and their derivatives.

Biochemical Characterization of a Novel Endo-1,3-β-Glucanase from the Scallop Chlamys farreri

Endo-1,3-β-glucanases derived from marine mollusks have attracted much attention in recent years because of their unique transglycosylation activity. In this study, a novel endo-1,3-β-glucanase from the scallop Chlamys farreri, named L_cf, was biochemically characterized. Unlike in earlier studies on marine mollusk endo-1,3-β-glucanases, L_cf was expressed in vitro first. Enzymatic analysis demonstrated that L_cf preferred to hydrolyze laminarihexaose than to hydrolyze laminarin. Furthermore, L_cf was capable of catalyzing transglycosylation reactions with different kinds of glycosyl acceptors. More interestingly, the transglycosylation specificity of L_cf was different from that of other marine mollusk endo-1,3-β-glucanases, although they share a high sequence identity. This study enhanced our understanding of the diverse enzymatic specificities of marine mollusk endo-1,3-β-glucanases, which facilitated development of a unique endo-1,3-β-glucanase tool in the synthesis of novel glycosides.

A Novel Digestive GH16 β-1,3(4)-Glucanase from the Fungus-Growing Termite Macrotermes barneyi

β-1,3-glucanases are the main digestive enzymes of plant and fungal cell wall. Transcriptomic analysis of the fungus-growing termite Macrotermes barneyi revealed a high expression of a predicted β-1,3(4)-glucanase (Mbbgl) transcript in termite gut. Here, we described the cDNA cloning, heterologous expression, and enzyme characterization of Mbbgl. Sequence analysis and RT-PCR results showed that Mbbgl is a termite-origin GH16 β-1,3(4)-glucanase. The recombinant enzyme showed the highest activity towards laminarin and was active optimally at 50 °C, pH 5.5. The enzyme displayed endo/exo β-1,3(4)-glucanase activities. Moreover, Mbbgl had weak transglycosylation activity. The results indicate that Mbbgl is an endogenous digestive β-1,3(4)-glucanase, which contributes to the decomposition of plant biomass and fungal hyphae. Additionally, the multiple activities, pH, and ion stabilities make Mbbgl a potential candidate for application in the food industry.

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.

Review: The structure and function of cellulase (endo-β-1,4-glucanase) and hemicellulase (β-1,3-glucanase and endo-β-1,4-mannase) enzymes in invertebrates that consume materials ranging from microbes, algae to leaf litter

This review discusses the reaction catalysed, and the structure and function of the cellulase, endo-β-1,4-glucanase and the hemicellulase enzymes, β-1,3-glucanase and endo-β-1,4-mannase that are present in numerous invertebrate groups with a diverse range of feeding specialisations. These range from microbial deposit and filter feeders, micro and macrophagous algal feeders, omnivores to herbivorous leaf litter and wood feeders. Endo-β-1,4-glucanase from glycosyl hydrolase family 9 (GH9) digests cellulose like β-1,4-glucans from a range of materials. As it hydrolyses crystalline cellulose very slowly, it is a poor cellulase. Where tested, the enzyme has dual endo-β-1,4-glucanase and lichenase activity. Its presence does not necessarily indicate the ability of an animal to digest cellulose. It only indicates the ability to digest β-1,4-glucans and its function, which is discussed in this review, should be considered with reference to the substrates present in the diet. β-1,3-glucanase (laminarinase) belongs to glycosyl hydrolase family 16 (GH16) and hydrolyses β-1.3-glucans. These polysaccharides are present in the cell walls of algae, protozoans and yeast, and they also occur as storage polysaccharides within protozoans and algae. Depending on their site of expression, these enzymes may function as a digestive enzyme or may be involved in innate immunity. Enzymes present in the digestive fluids or tissues, would be digestive. Haemolymph GH16 proteins may be involved in innate immunity through the activation of the phenol oxidase system. Insect GH16 proteins expressed within the haemolymph have lost their catalytic residues and function as β-glucan binding proteins. In contrast, crustacean GH16 proteins expressed within the same tissue, have retained the catalytic residues and thus possibly their β-1,3-glucanase activity. The potential function of which is discussed. Endo-β-1,4-mannase from glycosyl hydrolase family 5, subfamily 10 (GH5_10) hydrolyses mannan, glucomannan and galactomannan. These hemicelluloses are present in the cell walls of plants and algae and also function as storage polysaccharides within legume and palm seeds. They are digestive enzymes whose high expression in some species suggests they are a major contributor to hemicellulose digestion. They may also provide the animal with substantial amounts of monosaccharides for energy.

Metabolic response of yellow mealworm larvae to two alternative rearing substrates

INTRODUCTION

Mass insect rearing is becoming increasingly pursued by food and feed industry due to its high sustainability and low environmental impact. Yellow mealworm larvae (Tenebrio molitor) are conventionally reared on wheat bran (WB), but alternative substrates, such as several by-products of the agri-food industry, have shown good prospects for insect rearing.

OBJECTIVES

The objective of this study was to investigate on the metabolic and nutritional response of yellow mealworm larvae to dried brewer's spent grains (BSG) and WB used as rearing substrates.

METHODS

Proximate, fibre and fatty acid compositions of durum WB and dried BSG were first characterized. Mealworm larvae were fed either WB (WB-L) or BSG (BSG-L) in a trial reproducing a scale rearing condition. Feed efficiency parameters together with proximate and FA composition were determined. Metabolic pathways affected by the dietary treatments were evaluated by means of a targeted metabolomics approach. Proton nuclear magnetic resonance (¹H NMR) spectra were acquired on lipid and polar extracts of WB-L and BSG-L and then coupled to multivariate data analysis. Absolute quantitative ¹H NMR data were carried out on selected metabolites.

RESULTS

BSG-L exhibited better feed conversion ratio and efficiency in conversion of ingested food (P < 0.05) and almost half fat content (P < 0.001) than WB-L. BSG-L also showed higher ω-3 and ω-6 poliunsaturated fatty acids (P < 0.001) and lower content of monounsaturated fatty acids (P < 0.001) than WB-L. BSG-L mobilized body fat towards methylamine accumulation and led to enhanced trehalose catabolism.

CONCLUSIONS

Our findings are useful to gain knowledge on the metabolic features that finally affect growth and body composition in reared yellow mealworm larvae.

Biochemical and Functional Characterization of Glycoside Hydrolase Family 16 Genes in Aedes aegypti Larvae: Identification of the Major Digestive β-1,3-Glucanase

Insect β-1,3-glucanases belong to Glycoside Hydrolase Family 16 (GHF16) and are involved in digestion of detritus and plant hemicellulose. In this work, we investigated the role of GHF16 genes in Aedes aegypti larvae, due to their detritivore diet. Aedes aegypti genome has six genes belonging to GHF16 (Aae GH16.1 – Aae GH16.6), containing two to six exons. Sequence analysis suggests that five of these GHF16 sequences (Aae GH16.1, 2, 3, 5, and 6) contain the conserved catalytic residues of this family and correspond to glucanases. All genomes of Nematocera analyzed showed putative gene duplications corresponding to these sequences. Aae GH16.4 has no conserved catalytic residues and is probably a β-1,3-glucan binding protein involved in the activation of innate immune responses. Additionally, Ae. aegypti larvae contain significant β-1,3-glucanase activities in the head, gut and rest of body. These activities have optimum pH about 5–6 and molecular masses between 41 and 150 kDa. All GHF16 genes above showed different levels of expression in the larval head, gut or rest of the body. Knock-down of AeGH16.5 resulted in survival and pupation rates lower than controls (dsGFP and water treated). However, under stress conditions, severe mortalities were observed in AeGH16.1 and AeGH16.6 knocked-down larvae. Enzymatic assays of β-1,3-glucanase in AeGH16.5 silenced larvae exhibited lower activity in the gut and no change in the rest of the body. Chromatographic activity profiles from gut samples after GH16.5 silencing showed suppression of enzymatic activity, suggesting that this gene codes for the digestive larval β-1,3-glucanase of Ae. aegypti. This gene and enzyme are attractive targets for new control strategies, based on the impairment of normal gut physiology.

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.

Identification and expression profiling of novel plant cell wall degrading enzymes from a destructive pest of palm trees, Rhynchophorus ferrugineus

Plant cell wall degrading enzymes (PCWDEs) from insects were recently identified as a multigene family of proteins that consist primarily of glycoside hydrolases (GHs) and carbohydrate esterases (CEs) and play essential roles in the degradation of the cellulose/hemicellulose/pectin network in the invaded host plant. Here we applied transcriptomic and degenerate PCR approaches to identify the PCWDEs from a destructive pest of palm trees, Rhynchophorus ferrugineus, followed by a gut-specific and stage-specific differential expression analysis. We identified a total of 27 transcripts encoding GH family members and three transcripts of the CE family with cellulase, hemicellulase and pectinase activities. We also identified two GH9 candidates, which have not previously been reported from Curculionidae. The gut-specific quantitative expression analysis identified key cellulases, hemicellulases and pectinases from R. ferrugineus. The expression analysis revealed a pectin methylesterase, RferCE8u02, and a cellulase, GH45c34485, which showed the highest gut enriched expression. Comparison of PCWDE expression patterns revealed that cellulases and pectinases are significantly upregulated in the adult stages, and we observed specific high expression of the hemicellulase RferGH16c4170. Overall, our study revealed the potential of PCWDEs from R. ferrugineus, which may be useful in biotechnological applications and may represent new tools in R. ferrugineus pest management strategies.

Comparative genomic analysis of innate immunity reveals novel and conserved components in crustacean food crop species

BACKGROUND

Growing global demands for crustacean food crop species have driven large investments in aquaculture research worldwide. However, large-scale production is susceptible to pathogen-mediated destruction particularly in developing economies. Thus, a thorough understanding of the immune system components of food crop species is imperative for research to combat pathogens.

RESULTS

Through a comparative genomics approach utilising extant data from 55 species, we describe the innate immune system of the class Malacostraca, which includes all food crop species. We identify 7407 malacostracan genes from 39 gene families implicated in different aspects of host defence and demonstrate dynamic evolution of innate immunity components within this group. Malacostracans have achieved flexibility in recognising infectious agents through divergent evolution and expansion of pathogen recognition receptors genes. Antiviral RNAi, Toll and JAK-STAT signal transduction pathways have remained conserved within Malacostraca, although the Imd pathway appears to lack several key components. Immune effectors such as the antimicrobial peptides (AMPs) have unique evolutionary profiles, with many malacostracan AMPs not found in other arthropods. Lastly, we describe four putative novel immune gene families, potentially representing important evolutionary novelties of the malacostracan immune system.

CONCLUSION

Our analyses across the broader Malacostraca have allowed us to not only draw analogies with other arthropods but also to identify evolutionary novelties in immune modulation components and form strong hypotheses as to when key pathways have evolved or diverged. This will serve as a key resource for future immunology research in crustacean food crops.

Digestion of Yeasts and Beta-1,3-Glucanases in Mosquito Larvae: Physiological and Biochemical Considerations

Aedes aegypti larvae ingest several kinds of microorganisms. In spite of studies regarding mosquito digestion, little is known about the nutritional utilization of ingested cells by larvae. We investigated the effects of using yeasts as the sole nutrient source for A. aegypti larvae. We also assessed the role of beta-1,3-glucanases in digestion of live yeast cells. Beta-1,3-glucanases are enzymes which hydrolyze the cell wall beta-1,3-glucan polyssacharide. Larvae were fed with cat food (controls), live or autoclaved Saccharomyces cerevisiae cells and larval weight, time for pupation and adult emergence, larval and pupal mortality were measured. The presence of S. cerevisiae cells inside the larval gut was demonstrated by light microscopy. Beta-1,3-glucanase was measured in dissected larval samples. Viability assays were performed with live yeast cells and larval gut homogenates, with or without addition of competing beta-1,3-glucan. A. aegypti larvae fed with yeast cells were heavier at the 4^th instar and showed complete development with normal mortality rates. Yeast cells were efficiently ingested by larvae and quickly killed (10% death in 2h, 100% in 48h). Larvae showed beta-1,3-glucanase in head, gut and rest of body. Gut beta-1,3-glucanase was not derived from ingested yeast cells. Gut and rest of body activity was not affected by the yeast diet, but head homogenates showed a lower activity in animals fed with autoclaved S. cerevisiae cells. The enzymatic lysis of live S. cerevisiae cells was demonstrated using gut homogenates, and this activity was abolished when excess beta-1,3-glucan was added to assays. These results show that live yeast cells are efficiently ingested and hydrolyzed by A. aegypti larvae, which are able to fully-develop on a diet based exclusively on these organisms. Beta-1,3-glucanase seems to be essential for yeast lytic activity of A. aegypti larvae, which possess significant amounts of these enzyme in all parts investigated.

Expression pattern of glycoside hydrolase genes in Lutzomyia longipalpis reveals key enzymes involved in larval digestion

The sand fly Lutzomyia longipalpis is the most important vector of American Visceral Leishmaniasis. Adults are phytophagous (males and females) or blood feeders (females only), and larvae feed on solid detritus. Digestion in sand fly larvae has scarcely been studied, but some glycosidase activities putatively involved in microorganism digestion were already described. Nevertheless, the molecular nature of these enzymes, as the corresponding genes and transcripts, were not explored yet. Catabolism of microbial carbohydrates in insects generally involves β-1,3-glucanases, chitinases, and digestive lysozymes. In this work, the transcripts of digestive β-1,3-glucanase and chitinases were identified in the L. longipalpis larvae throughout analysis of sequences and expression patterns of glycoside hydrolases families 16, 18, and 22. The activity of one i-type lysozyme was also registered. Interestingly, this lysozyme seems to play a role in immunity, rather than digestion. This is the first attempt to identify the molecular nature of sand fly larval digestive enzymes.

Molecular evolution of glycoside hydrolase genes in the Western corn rootworm (Diabrotica virgifera virgifera)

Cellulose is an important nutritional resource for a number of insect herbivores. Digestion of cellulose and other polysaccharides in plant-based diets requires several types of enzymes including a number of glycoside hydrolase (GH) families. In a previous study, we showed that a single GH45 gene is present in the midgut tissue of the western corn rootworm, Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae). However, the presence of multiple enzymes was also suggested by the lack of a significant biological response when the expression of the gene was silenced by RNA interference. In order to clarify the repertoire of cellulose-degrading enzymes and related GH family proteins in D. v. virgifera, we performed next-generation sequencing and assembled transcriptomes from the tissue of three different developmental stages (eggs, neonates, and third instar larvae). Results of this study revealed the presence of seventy-eight genes that potentially encode GH enzymes belonging to eight families (GH45, GH48, GH28, GH16, GH31, GH27, GH5, and GH1). The numbers of GH45 and GH28 genes identified in D. v. virgifera are among the largest in insects where these genes have been identified. Three GH family genes (GH45, GH48, and GH28) are found almost exclusively in two coleopteran superfamilies (Chrysomeloidea and Curculionoidea) among insects, indicating the possibility of their acquisitions by horizontal gene transfer rather than simple vertical transmission from ancestral lineages of insects. Acquisition of GH genes by horizontal gene transfers and subsequent lineage-specific GH gene expansion appear to have played important roles for phytophagous beetles in specializing on particular groups of host plants and in the case of D. v. virgifera, its close association with maize.

Nest sanitation through defecation: antifungal properties of wood cockroach feces

The wood cockroach Cryptocercus punctulatus nests as family units inside decayed wood, a substrate known for its high microbial load. We tested the hypothesis that defecation within their nests, a common occurrence in this species, reduces the probability of fungal development. Conidia of the entomopathogenic fungus, Metarhizium anisopliae, were incubated with crushed feces and subsequently plated on potato dextrose agar. Relative to controls, the viability of fungal conidia was significantly reduced following incubation with feces and was negatively correlated with incubation time. Although the cockroach's hindgut contained abundant β-1,3-glucanase activity, its feces had no detectable enzymatic function. Hence, these enzymes are unlikely the source of the fungistasis. Instead, the antifungal compound(s) of the feces involved heat-sensitive factor(s) of potential microbial origin. When feces were boiled or when they were subjected to ultraviolet radiation and subsequently incubated with conidia, viability was "rescued" and germination rates were similar to those of controls. Filtration experiments indicate that the fungistatic activity of feces results from chemical interference. Because Cryptocercidae cockroaches have been considered appropriate models to make inferences about the factors fostering the evolution of termite sociality, we suggest that nesting in microbe-rich environments likely selected for the coupling of intranest defecation and feces fungistasis in the common ancestor of wood cockroaches and termites. This might in turn have served as a preadaptation that prevented mycosis as these phylogenetically related taxa diverged and evolved respectively into subsocial and eusocial organizations.

Endogenous Plant Cell Wall Digestion: A Key Mechanism in Insect Evolution

The prevailing view that insects lack endogenous enzymes for plant cell wall (PCW) digestion had led to the hypothesis that PCW digestion evolved independently in different insect taxa through the establishment of symbiotic relationships with microorganisms. However, recent studies reporting endogenous PCW-degrading genes and enzymes for several insects, including phylogenetically basal insects and closely related arthropod groups, challenge this hypothesis. Here, we summarize the molecular and biochemical evidence on the mechanisms of PCW digestion in insects to analyze its evolutionary pathways. The evidence reveals that the symbiotic-independent mechanism may be the ancestral mechanism for PCW digestion. We discuss the implications of this alternative hypothesis in the evolution of plant-insect interactions and suggest that changes in the composition of lignocellulolytic complexes were involved in the evolution of feeding habits and diet specializations in insects, playing important roles in the evolution of plant-insect interactions and in the diversification of insects.

Relationship between digestive enzymes and food habit of Lutzomyia longipalpis (Diptera: Psychodidae) larvae: Characterization of carbohydrases and digestion of microorganisms

The sandfly Lutzomyia longipalpis (Lutz and Neiva, 1912) is the main vector of American Visceral Leishmaniasis. In spite of its medical importance and several studies concerning adult digestive physiology, biochemistry and molecular biology, very few studies have been carried out to elucidate the digestion in sandfly larvae. Even the breeding sites and food sources of these animals in the field are largely uncharacterized. In this paper, we describe and characterize several carbohydrases from the gut of L. longipalpis larvae, and show that they are probably not acquired from food. The enzyme profile of this insect is consistent with the digestion of fungal and bacterial cells, which were proved to be ingested by larvae under laboratory conditions. In this respect, sandfly larvae might have a detritivore habit in nature, being able to exploit microorganisms usually encountered in the detritus as a food source.

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).

Subterranean termite prophylactic secretions and external antifungal defenses

Termites exploit environments that make them susceptible to infection and rapid disease transmission. Gram-negative bacteria binding proteins (GNBPs) signal the presence of microbes and in some insects directly damage fungal pathogens with β-1,3-glucanase activity. The subterranean termites Reticulitermes flavipes and Reticulitermes virginicus encounter soil entomopathogenic fungi such as Metarhizium anisopliae, which can evade host immune responses after penetrating the cuticle. An external defense that prevents invasion of fungal pathogens could be crucial in termites, allowing them to thrive under high pathogenic pressures. We investigated the role of secreted β-1,3-glucanases in Reticulitermes defenses against M. anisopliae. Our results show that these termites secrete antifungal β-1,3-glucanases on the cuticle, and the specific inhibition of GNBP associated β-1,3-glucanase activity with d-δ-gluconolactone (GDL) reduces this activity and can cause significant increases in mortality after exposure to M. anisopliae. Secreted β-1,3-glucanases appear to be essential in preventing infection by breaking down fungi externally.

Characterization of a β-1,3-glucanase active in the alkaline midgut of Spodoptera frugiperda larvae and its relation to β-glucan-binding proteins

Spodoptera frugiperda β-1,3-glucanase (SLam) was purified from larval midgut. It has a molecular mass of 37.5 kDa, an alkaline optimum pH of 9.0, is active against β-1,3-glucan (laminarin), but cannot hydrolyze yeast β-1,3-1,6-glucan or other polysaccharides. The enzyme is an endoglucanase with low processivity (0.4), and is not inhibited by high concentrations of substrate. In contrast to other digestive β-1,3-glucanases from insects, SLam is unable to lyse Saccharomyces cerevisae cells. The cDNA encoding SLam was cloned and sequenced, showing that the protein belongs to glycosyl hydrolase family 16 as other insect glucanases and glucan-binding proteins. Multiple sequence alignment of β-1,3-glucanases and β-glucan-binding protein supports the assumption that the β-1,3-glucanase gene duplicated in the ancestor of mollusks and arthropods. One copy originated the derived β-1,3-glucanases by the loss of an extended N-terminal region and the β-glucan-binding proteins by the loss of the catalytic residues. SLam homology modeling suggests that E228 may affect the ionization of the catalytic residues, thus displacing the enzyme pH optimum. SLam antiserum reacts with a single protein in the insect midgut. Immunocytolocalization shows that the enzyme is present in secretory vesicles and glycocalyx from columnar cells.