Action pattern, specificity, lytic activities, and physiological role of five digestive beta-glucanases isolated from Periplaneta americana

Potential of insect endogenous cellulases for lignocellulosic break down deciphered using molecular docking studies

Insects possess cellulolytic system capable of producing variegate enzymes with multifarious specificities to break down complex lignocellulosic products. Astonishingly, endoglucanases, exoglucanases and β-glycosidases act sequentially in a synergistic system to facilitate the breakdown of cellulose to utilisable energy source glucose. In silico docking studies of endo-β-1,4-glucanase from 19 different insects belonging to six different orders identified that it possesses high affinity for all the six substrates, including CMC, cellulose, cellotriose, cellotetraose, cellopentose and cellohexaose. Additionally, β-glucosidase from nearly all the reported insect sources also showed considerable affinity towards cellobiose. Van der Waals, conventional hydrogen bonds and carbon-hydrogen bonds stabilise the interaction between the enzyme and different substrates. Molecular dynamics simulations also held up the stability of various complexes. Efficient breakdown of lignocelluloses-based substrates becoming a major focus of industrial and academic communities worldwide, this study can perhaps complement the propensity of insect cellulases for prospected applications.

Predominant contribution of an endogenous cellulase (OlCel) to the cellulolysis in the digestive system of larvae of banana pseudostem weevil, Odoiporus longicollis (Coleoptera: Curculionidae)

Insects have evolved with effective strategies to utilize cellulose as an energy source by possessing cellulolytic enzymes which can be used as an optimal resource in the bioenergy sector. The study was aimed at evaluating the cellulolytic enzyme in the larval gut of the banana pseudostem weevil, Odoiporus longicollis Olivier (Coleoptera: Curculionidae). Primarily, cellulase activity was localized along the gut, in which the midgut showed the highest activity (2858 U/mg). The thermo-tolerance of cellulase activity was found to be up to 80°C (highest at 60°C), and the enzyme was stable at a pH between 5 and 6. Various concentrations of divalent cations (CaCl2 , MgCl2 , and CuCl2 ) have differential enhancing and inhibitory effects on cellulase activity. The cellulase (OlCel) was purified using anion exchange chromatography. The molecular weight of the cellulase was determined to be 47 kDa. The physicochemical parameters of the purified enzyme were similar to that of enzyme activity of whole gut extract. Mass spectrometry results identified sequence similarities of purified cellulase to the glycosyl hydrolase family 5 (GHF5) family. The gut microbial cellulase activity as exogenous source showed no competence compared with the endogenous activity.

Utility of cockroach as a model organism in the assessment of toxicological impacts of environmental pollutants

Environmental pollution is a global concern because of its associated risks to human health and ecosystem. The bio-monitoring of environmental health has attracted much attention in recent years and efforts to minimize environmental contamination as well as to delineate toxicological mechanisms related to toxic exposure are essential to improve the health conditions of both humans and animals. This review aims to substantiate the need and advantages in utilizing cockroaches as a complementary, non-mammalian model to further understand the noxious impact of environmental contaminants on humans and animals. We discuss recent advances in neurotoxicology, immunotoxicology, reproductive and developmental toxicology, environmental forensic entomotoxicology, and environmental toxicology that corroborate the utility of the cockroach (Periplaneta americana, Blaptica dubia, Blattella germanica and Nauphoeta cinerea) in addressing toxicological mechanisms as well as a sensor of environmental pollution. Indeed, recent improvements in behavioural assessment and the detection of potential biomarkers allow for the recognition of phenotypic alterations in cockroaches following exposure to toxic chemicals namely saxitoxin, methylmercury, polychlorinated biphenyls, electromagnetic fields, pharmaceuticals, polycyclic aromatic hydrocarbon, chemical warfare agents and nanoparticles. The review provides a state-of-the-art update on the current utility of cockroach models in various aspects of toxicology as well as discusses the potential limitations and future perspectives.

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.

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.

Evolutionary trends of digestion and absorption in the major insect orders

The spatial organization of digestion, which corresponds to the steps by which the ingested food is hydrolyzed in the different regions of the gut, was described in insects from the major insect orders. The pattern of digestion and absorption in the midgut shows a strong phylogenetic influence, modulated by adaptation to particular feeding habits. Based on this, basic digestive patterns were recognized and were proposed to represent the major ancestors from which the different orders evolved. The putative ancestors chosen to represent different points in the evolution from basal Neoptera to more derived orders were: Neoptera, Polyneoptera, Hemiptera, Hymenoptera-Panorpoidea (Diptera-Lepidoptera), Lepidoptera, and Cyclorrhapha. The basic plan of Neoptera was supposed to be alike that of Polyneoptera, which was hypothesized from studies performed in grasshoppers, crickets and from stick insects. For Holometabola, the basic plan was initially proposed from studies carried out in beetles, bees, nematocerous flies, common flies and also from moths. This review updates the physiological data supporting the putative midgut basic patterns by discussing available data on insects pertaining to different taxa and details the evolutionary trends of midgut function among the major insect orders. Furthermore, by using recent genomic and transcriptome data, this review discusses the few insects for which the spatial organization of midgut absorption is known.

Cultivable, Host-Specific Bacteroidetes Symbionts Exhibit Diverse Polysaccharolytic Strategies

Beneficial gut microbes can facilitate insect growth on diverse diets. The omnivorous American cockroach, Periplaneta americana (Insecta: Blattodea), thrives on a diet rich in plant polysaccharides and harbors a species-rich gut microbiota responsive to host diet. Bacteroidetes are among the most abundant taxa in P. americana and other cockroaches, based on cultivation-independent gut community profiling, and these potentially polysaccharolytic bacteria may contribute to host diet processing. Eleven Bacteroidetes isolates were cultivated from P. americana digestive tracts, and phylogenomic analyses suggest that they were new Bacteroides, Dysgonomonas, Paludibacter, and Parabacteroides species distinct from those previously isolated from other insects, humans, and environmental sources. In addition, complete genomes were generated for each isolate, and polysaccharide utilization loci (PULs) and several non-PUL-associated carbohydrate-active enzyme (CAZyme)-coding genes that putatively target starch, pectin, and/or cellulose were annotated in each of the isolate genomes. Type IX secretion system (T9SS)- and CAZyme-coding genes tagged with the corresponding T9SS recognition and export C-terminal domain were observed in some isolates, suggesting that these CAZymes were deployed via non-PUL outer membrane translocons. Additionally, single-substrate growth and enzymatic assays confirmed genomic predictions that a subset of the Bacteroides and Dysgonomonas isolates could degrade starch, pectin, and/or cellulose and grow in the presence of these substrates as a single sugar source. Plant polysaccharides enrich P. americana diets, and many of these gut isolates are well equipped to exploit host dietary inputs and potentially contribute to gut community and host nutrient accessibility.IMPORTANCE Gut microbes are increasingly being recognized as critical contributors to nutrient accessibility in animals. The globally distributed omnivorous American cockroach (Periplaneta americana) harbors many bacterial phyla (e.g., Bacteroidetes) that are abundant in vertebrates. P. americana thrives on a highly diverse plant-enriched diet, making this insect a rich potential source of uncharacterized polysaccharolytic bacteria. We have cultivated, completely sequenced, and functionally characterized several novel Bacteroidetes species that are endemic to the P. americana gut, and many of these isolates can degrade simple and complex polysaccharides. Cultivation and genomic characterization of these Bacteroidetes isolates further enable deeper insight into how these taxa participate in polysaccharide metabolism and, more broadly, how they affect animal health and development.

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.

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.

Immune functions of insect βGRPs and their potential application

Insects rely completely on the innate immune system to sense the foreign bodies and to mount the immune responses. Germ-line encoded pattern recognition receptors play crucial roles in recognizing pathogen-associated molecular patterns. Among them, β-1,3-glucan recognition proteins (βGRPs) and gram-negative bacteria-binding proteins (GNBPs) belong to the same pattern recognition receptor family, which can recognize β-1,3-glucans. Typical insect βGRPs are comprised of a tandem carbohydrate-binding module in the N-terminal and a glucanase-like domain in the C-terminal. The former can recognize triple-helical β-1,3-glucans, whereas the latter, which normally lacks the enzymatic activity, can recruit adapter proteins to initiate the protease cascade. According to studies, insect βGRPs possess at least three types of functions. Firstly, some βGRPs cooperate with peptidoglycan recognition proteins to recognize the lysine-type peptidoglycans upstream of the Toll pathway. Secondly, some directly recognize fungal β-1,3-glucans to activate the Toll pathway and melanization. Thirdly, some form the 'attack complexes' with other immune effectors to promote the antifungal defenses. The current review will focus on the discovery of insect βGRPs, functions of some well-characterized members, structure-function studies and their potential application.

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.

A Novel Use for Potassium Alum as Controlling Agent Against Periplaneta americana (Dictyoptera: Blattidae)

In this work, we present our results on the use of potassium alum as an environmentally friendly insecticide. This compound has the potential to rid our homes, schools, hotels, restaurants, and ships of cockroach infestations. This compound is environmentally friendly and has no hazardous effects on plant, animal, or human ecosystems. Alum was approved for medical use a long time ago. In our laboratory, we developed a novel method using potassium alum as an environmentally friendly insecticide to kill the most common cockroach in the subtropical region, Periplaneta americana (L.). Adult and nymph-staged cockroaches were left to feed on potassium alum per individual insect after a period of food deprivation. The mortality was recorded as LT50. The younger nymphs the third and early fourth instars died within 4 d of feeding after consuming an average of 0.3 mg per individual insect. Gravid females were highly susceptible to alum toxicity and experienced a higher mortality rate, with an average of 3 mg per individual female. The oothecae of the normal untreated females were 8.1 mm long and 4.13 mm wide and weighed 94 mg. The eggs laid by the treated gravid females were underweight and exhibited a dwarfism shape, and these eggs did not hatched if the females consumed the potassium alum before laying eggs. The results revealed that the adult male and female cockroaches have to consume 1 mg and 2.7 mg, respectively, of potassium alum to kill 100% of them after 1 month of ingestion. The potassium alum had to be ingested by the cockroaches to affect mortality. The effect of potassium alum was attributed to chronic toxicity and not acute toxicity. The potential applications of this novel technique will be discussed.

Characterization of α-L-fucosidase and other digestive hydrolases from Biomphalaria glabrata

Schistosoma mansoni is one of the major agents of the disease Schistosomiasis, which is one of the major global public health concerns. Biomphalaria glabrata is an obligate intermediate mollusc host of S. mansoni. Although the development of S. mansoni occurs in the snail hepatopancreas, studies that focus on this organ remain limited. In this study, we biochemically identified five distinct carbohydrases (amylase, maltase, α-glucosidase, trehalase, and α-L-fucosidase), lipases, and peptidases in the B. glabrata hepatopancreas and focused on the isolation and characterization of the activity of α-L-fucosidase. The isolated α-L-fucosidase has a molecular mass of 141 kDa, an optimum pH of 5.8, and is inhibited by Tris, fucose, and 1-deoxyfuconojirimycin. B. glabrata α-L-fucosidase is an exoglycosidase that can hydrolyze the natural substrate fucoidan to fucose residues. It presented Km values of 48.4 μM to 4-Methylumbelliferyl α-L-fucopyranoside and 0.55 mM to p-nitrophenyl-α-L-fucopyranoside. Thus, α-L-fucosidase has a high activity in the hepatopancreas of B. glabrata, and the differential expression of this enzyme between susceptible and resistant strains indicates that besides its digestive role, α-L-fucosidase may also be important in host/parasite interactions.

Physiology of digestion and the molecular characterization of the major digestive enzymes from Periplaneta americana

Cockroaches are among the first insects to appear in the fossil record. This work is part of ongoing research on insects at critical points in the evolutionary tree to disclose evolutionary trends in the digestive characteristics of insects. A transcriptome (454 Roche platform) of the midgut of Periplanetaamericana was searched for sequences of digestive enzymes. The selected sequences were manually curated. The complete or nearly complete sequences showing all characteristic motifs and highly expressed (reads counting) had their predicted sequences checked by cloning and Sanger sequencing. There are two chitinases (lacking mucin and chitin-binding domains), one amylase, two α- and three β-glucosidases, one β-galactosidase, two aminopeptidases (none of the N-group), one chymotrypsin, 5 trypsins, and none β-glucanase. Electrophoretic and enzymological data agreed with transcriptome data in showing that there is a single β-galactosidase, two α-glucosidases, one preferring as substrate maltase and the other aryl α-glucoside, and two β-glucosidases. Chromatographic and enzymological data identified 4 trypsins, one chymotrypsin (also found in the transcriptome), and one non-identified proteinase. The major digestive trypsin is identifiable to a major P. americana allergen (Per a 10). The lack of β-glucanase expression in midguts was confirmed, thus lending support to claims that those enzymes are salivary. A salivary amylase was molecularly cloned and shown to be different from the one from the midgut. Enzyme distribution showed that most digestion occurs under the action of salivary and midgut enzymes in the foregut and anterior midgut, except the posterior terminal digestion of proteins. A counter-flux of fluid may be functional in the midgut of the cockroach to explain the low excretory rate of digestive enzymes. Ultrastructural and immunocytochemical localization data showed that amylase and trypsin are released by both merocrine and apocrine secretion mainly from gastric caeca. Finally, a discussion on Polyneoptera digestive physiology is provided.

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.

Bacterial community composition shifts in the gut of Periplaneta americana fed on different lignocellulosic materials

Abstract

Cockroaches are insects that can accommodate diets of different composition, including lignocellulosic materials. Digestion of these compounds is achieved by the insect’s own enzymes and also by enzymes produced by gut symbionts. The presence of different and modular bacterial phyla on the cockroach gut tract suggests that this insect could be an interesting model to study the organization of gut bacterial communities associated with the digestion of different lignocellulosic diets. Thus, changes in the diversity of gut associated bacterial communities of insects exposed to such diets could give useful insights on how to improve hemicellulose and cellulose breakdown systems. In this work, through sequence analysis of 16S rRNA clone libraries, we compared the phylogenetic diversity and composition of gut associated bacteria in the cockroach Periplaneta americana collected in the wild-types or kept on two different diets: sugarcane bagasse and crystalline cellulose. These high fiber diets favor the predominance of some bacterial phyla, such as Firmicutes, when compared to wild-types cockroaches. Our data show a high bacterial diversity in P. americana gut, with communities composed mostly by the phyla Bacteroidetes, Firmicutes, Proteobacteria and Synergistetes. Our data show that the composition and diversity of gut bacterial communities could be modulated by diet composition. The increased presence of Firmicutes in sugarcane bagasse and crystalline cellulose-fed animals suggests that these bacteria are strongly involved in lignocellulose digestion in cockroach guts.

Background

Cockroaches are omnivorous animals that can incorporate in their diets food of different composition, including lignocellulosic materials. Digestion of these compounds is achieved by the insect’s own enzymes and also by enzymes produced by gut symbiont. However, the influence of diet with different fiber contents on gut bacterial communities and how this affects the digestion of cockroaches is still unclear. The presence of some bacterial phyla on gut tract suggests that cockroaches could be an interesting model to study the organization of gut bacterial communities during digestion of different lignocellulosic diets. Knowledge about the changes in diversity of gut associated bacterial communities of insects exposed to such diets could give interesting insights on how to improve hemicellulose and cellulose breakdown systems.

Methodology/principal findings

We compared the phylogenetic diversity and composition of gut associated bacteria in the cockroach P. americana caught on the wild or kept on two different diets: sugarcane bagasse and crystalline cellulose. For this purpose we constructed bacterial 16S rRNA gene libraries which showed that a diet rich in cellulose and sugarcane bagasse favors the predominance of some bacterial phyla, more remarkably Firmicutes, when compared to wild cockroaches. Rarefaction analysis, LIBSHUFF and UniFrac PCA comparisons showed that gene libraries of wild insects were the most diverse, followed by sugarcane bagasse fed and then cellulose fed animals. It is also noteworthy that cellulose and sugarcane bagasse gene libraries resemble each other.

Conclusion/significance

Our data show a high bacterial diversity in P. americana gut, with communities composed mostly by the phyla Bacteroidetes, Firmicutes, Proteobacteria and Synergistetes. The composition and diversity of gut bacterial communities could be modulated by font of diet composition. The increased presence of Firmicutes in sugarcane bagasse and crystalline cellulose-fed animals suggests that these bacteria are strongly involved in lignocellulose digestion in cockroach guts.

Carbohydrate digestion in ticks and a digestive α-L-fucosidase

Digestive carbohydrases are present in many species of hematophagous Arthropoda, including ticks. In this work, Amblyomma cajennense (Ixodidae) midgut digestive carbohydrases were tracked with different substrates, resulting in the identification of a chitinase and an N-acetyl-β-glucosaminidase and the first description of a digestive α-L-fucosidase in ticks. α-L-fucosidases are involved in various physiological processes, and digestive α-L-fucosidases have been shown to be present in other types of organisms. Amblyomma cajennense α-L-fucosidase activity was isolated using acidic and salting-out precipitations and chromatographic steps in hydrophobic and cation-exchange columns. The specificity of the isolated activity as an α-L-fucosidase was confirmed by the hydrolysis of 4-methylumbelliferyl α-L-fucopyranoside and the natural substrate fucoidan and the inhibition by fucose and deoxyfuconojirimycin. The isolated activity of α-L-fucosidase forms oligomers with molecular mass of 140 kDa or 150 kDa as determined by gel filtration and non-reducing SDS-PAGE, respectively. This particular fucosidase has an optimum pH of 5.3, is stable even at high temperatures (stable for at least 2h at 50 °C), has a Km of 45 μM to the substrate 4-methylumbelliferyl α-L-fucopyranoside and IC 50% of 327 μM to fucose and 42 pM to deoxyfuconojirimycin. The presence of digestive fucosidases in hematophagous Arthropoda may be related to defence mechanisms against host-parasite interactions.

Active site characterization and molecular cloning of Tenebrio molitor midgut trehalase and comments on their insect homologs

The soluble midgut trehalase from Tenebrio molitor (TmTre1) was purified after several chromatographic steps, resulting in an enzyme with 58 kDa and pH optimum 5.3 (ionizing active groups in the free enzyme: pK(e1) = 3.8 ± 0.2 pK(e2) = 7.4 ± 0.2). The purified enzyme corresponds to the deduced amino acid sequence of a cloned cDNA (TmTre1-cDNA), because a single cDNA coding a soluble trehalase was found in the T. molitor midgut transcriptome. Furthermore, the mass of the protein predicted to be coded by TmTre1-cDNA agrees with that of the purified enzyme. TmTre1 has the essential catalytic groups Asp 315 and Glu 513 and the essential Arg residues R164, R217, R282. Carbodiimide inactivation of the purified enzyme at different pH values reveals an essential carboxyl group with pKa = 3.5 ± 0.3. Phenylglyoxal modified a single Arg residue with pKa = 7.5 ± 0.2, as observed in the soluble trehalase from Spodoptera frugiperda (SfTre1). Diethylpyrocarbonate modified a His residue that resulted in a less active enzyme with pK(e1) changed to 4.8 ± 0.2. In TmTre1 the modified His residue (putatively His 336) is more exposed than the His modified in SfTre1 (putatively His 210) and that affects the ionization of an Arg residue. The architecture of the active site of TmTre1 and SfTre1 is different, as shown by multiple inhibition analysis, the meaning of which demands further research. Trehalase sequences obtained from midgut transcriptomes (pyrosequencing and Illumina data) from 8 insects pertaining to 5 different orders were used in a cladogram, together with other representative sequences. The data suggest that the trehalase gene went duplication and divergence prior to the separation of the paraneopteran and holometabolan orders and that the soluble trehalase derived from the membrane-bound one by losing the C-terminal transmembrane loop.

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.

A novel exo-cellulase from white spotted longhorn beetle (Anoplophora malasiaca)

Wood feeding insects depends heavily on the secretion of a combination of cellulases, mainly endoglucanases and other glucanases such as exoglucanases and xylanases, for efficient digestion of the cellulosic materials. To date, although a high number of endoglucanases have been found in xytophagous insects, little is known about exoglucanases encoded in the genome of these insects. Here we report the identification and isolation of an exoglucanase, designated as AmCel-5B, from the white spotted longhorn beetle, Anoplophora malasiaca. The optimal condition of enzymatic activity was found to be 50 °C and pH 4.0. Interestingly, this enzyme is not only exhibited exo-β-glucanase activity, but also with obvious endo-β-glucanase activity. Furthermore, this enzyme is unique in that, although it recognizes Avicel, evidenced as an exo-β-glucanase, it cannot recognize oligosaccharides smaller than cellohexaose. This may explain why longhorn beetle can well digest hard "living" wood, which contains primarily rigid long fibers. Although it is known that metal ions can enhance the activity of some cellulases, we further demonstrated that reducing agent could work synergistically with metal ions for significant activity enhancement of AmCel-5B. The discovery and investigation of an insect exoglucanase should lead to a greater understanding of the mechanism for efficient digestion of cellulosic materials by wood feeding insects, as well as facilitate their potential applications in the production of bioenergy and biomaterials from lignocellulosic biomass in the future.

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.

Longterm persistence of proteolytic activities in frass of Blattella germanica increases its allergenic potential

Chromogenic microplate assays in 96 wells were used to determine the stability of enzyme activity in frass of Blattella germanica (Blattodea: Blattellidae). Frass samples were exposed to controlled conditions [temperature 15-35 °C and/or 53-100% relative humidity (RH)] and to household conditions (apartment). Exposure times were 0 (control), 90, 183 and 276 days. Starch digestion and cellulolytic activities decreased during exposure. Non-specific proteolytic activities were affected by changes in selective proteolytic activities. Activities towards AAPpNA and SA(3) pNA strongly increased at 100% RH, indicating the possible influence of microorganisms growing on frass. Activities towards BApNA and ArgpNA decreased with increasing decomposition time, whereas activity towards ZRRpNA was not influenced by exposure time. The largest decrease in activities towards ArgpNA and BApNA occurred at temperatures of 15 °C, 30 °C and 35 °C and at 100% RH. Activities towards BApNA and ZRRpNA were very stable under different temperature and RH conditions; this was confirmed by findings showing that these activities were stable in the experimental apartment. In comparison with the control, activities towards ZRRpNA and BApNA after 276 days decreased by 1% and 19%, respectively. The longterm persistence of proteolytic activities in cockroach frass increases their allergenic hazard potential.

Recognition of microbial molecular patterns and stimulation of prophenoloxidase activation by a β-1,3-glucanase-related protein in Manduca sexta larval plasma

Detection of pathogenic invaders is the essential first step of a successful defense response in multicellular organisms. In this study, we have identified a new member of the β-1,3-glucanase-related protein superfamily from the tobacco hornworm Manduca sexta. This protein, designated microbe binding protein (MBP), is 61% identical in sequence to Bombyx mori Gram-negative bacteria binding protein, but only 34-36% identical to M. sexta β-1,3-glucan recognition protein-1 and 2. Its mRNA levels were strongly up-regulated in hemocytes and fat body of immune challenged larvae, along with an increase in concentration of the plasma protein. We expressed M. sexta MBP in a baculovirus-insect cell system. The purified protein associated with intact bacteria and fungi. It specifically bound to lipoteichoic acid, lipopolysaccharide, diaminopimelic acid-type peptidoglycans (DAP-PGs) from Escherichia coli and Bacillus subtilis, but less so to laminarin or Lys-type PG from Staphylococcus aureus. The complex binding pattern was influenced by other plasma factors and additional microbial surface molecules. After different amounts of MBP had been incubated with larval plasma on ice, a concentration-dependent increase in phenoloxidase (PO) activity occurred in the absence of any microbial elicitor. The activity increase was also observed in the mixture of plasma and a bacterial or fungal cell wall component. The prophenoloxidase (proPO) activation became more prominent when DAP-PGs, Micrococcus luteus Lys-PG, or lipoteichoic acid was included in the mixture of MBP and plasma. Statistic analysis suggested that a synergistic enhancement of proPO activation was caused by an interaction between MBP and these elicitors, but not S. aureus Lys-PG, lipopolysaccharide, curdlan, or laminarin. These data indicate that M. sexta MBP is a component of the surveillance mechanism and, by working together with other pattern recognition molecules and serine proteinases, triggers the proPO activation system.

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.

The last piece in the cellulase puzzle: the characterisation of beta-glucosidase from the herbivorous gecarcinid land crab Gecarcoidea natalis

A 160 kDa enzyme with beta-glucosidase activity was purified from the midgut gland of the land crab Gecarcoidea natalis. The enzyme was capable of releasing glucose progressively from cellobiose, cellotriose or cellotetraose. Although beta-glucosidases (EC 3.2.1.21) have some activity towards substrates longer than cellobiose, the enzyme was classified as a glucohydrolase (EC 3.2.1.74) as it had a preference for larger substrates (cellobiose<cellotriose=cellotetraose). It was able to synthesise some cellotetraose by the transglycosylation of smaller substrates - another common feature of glucohydrolases. The interaction between the glucohydrolase described here and the endo-beta-1,4-glucanases described previously for G. natalis provides a complete model for cellulose hydrolysis in crustaceans and possibly in other invertebrates. After mechanical fragmentation by the gastric mill, multiple endo-beta-1,4-glucanases would initially cleave beta-1,4-glycosidic bonds within native cellulose, releasing small oligomers, including cellobiose, cellotriose and cellotetraose. The glucohydrolase would then attach to these oligomers, progressively releasing glucose. The glucohydrolase might also attach directly to crystalline cellulose to release glucose from free chain ends. This two-enzyme system differs from the traditional model, which suggests that total cellulose hydrolysis requires the presence an endo-beta-1,4-glucanse, a cellobiohydrolase and a beta-glucosidase.

cDNA cloning, homology modelling and evolutionary insights into novel endogenous cellulases of the borer beetle Oncideres albomarginata chamela (Cerambycidae)

Novel endogenous cDNAs of beta-1, 4-endoglucanases (Oa-EGase I and Oa-EGase II) were cloned from the cerambycid beetle Oncideres albomarginata chamela. Oa-EGase I- and Oa-EGase II-deduced proteins and three-dimensional structures possess all features, including general architecture, signature motifs and catalytic domains, of glycosyl hydrolase families 5 and 45 (GHF5 and GHF45) and also share high levels of homology with other beetle cellulases. Total carboxymethylcellulase activity of O. a. chamela was 208.13 U/g of larvae. Phylogenetic analyses suggest that insect GHF5 and GHF45 are very ancient gene families and indicate, at least in the case of GHF5, that this family likely evolved from a common ancestor rather than, as is often reported, via horizontal gene transfer. Beetle GHF45 cellulases did not cluster with other metazoan cellulases. However, the presence of GHF45 cellulases in ancient molluscan taxa puts into question the hypothesis of horizontal gene transfer for the evolution of cellulases in animals.

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

The major beta-1,3-glucanase from Tenebrio molitor (TLam) was purified to homogeneity (yield, 6%; enrichment, 113 fold; specific activity, 4.4 U/mg). TLam has a molecular weight of 50 kDa and a pH optimum of 6. It is an endoglucanase that hydrolyzes beta-1,3-glucans as laminarin and yeast beta-1,3-1,6-glucan, but is inactive toward other polysaccharides (as unbranched beta-1,3-glucans or mixed beta-1,3-1,4-glucan from cereals) or disaccharides. The enzyme is not inhibited by high substrate concentrations and has low processivity (0.6). TLam has two ionizable groups involved in catalysis, and His, Tyr and Arg residues plus a divalent ion at the active site. A Cys residue important for TLam activity is exposed after laminarin binding. The cDNA coding for this enzyme was cloned and sequenced. It belongs to glycoside hydrolase family 16, and is related to other insect glucanases and glucan-binding proteins. Sequence analysis and homology modeling allowed the identification of some residues (E174, E179, H204, Y304, R127 and R181) at the active site of the enzyme, which may be important for TLam activity. TLam efficiently lyses fungal cells, suggesting a role in making available walls and cell contents to digestion and in protecting the midgut from pathogen infections.

Peptidase inhibitors from the salivary glands of the cockroach Nauphoeta cinerea

Inhibitory activity against subtilisin, proteinase K, chymotrypsin and trypsin was detected in the salivary glands and saliva of the cockroach Nauphoeta cinerea (Blattoptera: Blaberidae). Fractionation of the salivary glands extract by affinity chromatography followed by reverse-phase HPLC yielded five subtilisin-inhibiting peptides with molecular masses ranging from 5 to 14 kDa. N-terminal sequences and subsequently full-length cDNAs of inhibitors designated NcPIa and NcPIb were obtained. The NcPIa cDNA contains 216 nucleotides and encodes a pre-peptide of 72 amino-acid residues of which 19 make up the signal peptide. The cDNA of NcPIb consists of 240 nucleotides and yields a putative secretory peptide of 80 amino-acid residues. Mature NcPIa (5906.6 Da, 53 residues) and NcPIb (6713.3 Da, 60 residues) are structurally similar (65.4% amino acid overlap) single-domain Kazal-type peptidase inhibitors. NcPIa with Arg in P1 position and typical Kazal motif VCGSD interacted stoichiometrically (1:1) with subtilisin and was slightly less active against proteinase K. NcPIb with Leu in P1 and modified Kazal motif ICGSD had similar activity on subtilisin and no on proteinase K but was active on chymotrypsin.

Targeting an antimicrobial effector function in insect immunity as a pest control strategy

Insect pests such as termites cause damages to crops and man-made structures estimated at over $30 billion per year, imposing a global challenge for the human economy. Here, we report a strategy for compromising insect immunity that might lead to the development of nontoxic, sustainable pest control methods. Gram-negative bacteria binding proteins (GNBPs) are critical for sensing pathogenic infection and triggering effector responses. We report that termite GNBP-2 (tGNBP-2) shows beta(1,3)-glucanase effector activity previously unknown in animal immunity and is a pleiotropic pattern recognition receptor and an antimicrobial effector protein. Termites incorporate this protein into the nest building material, where it functions as a nest-embedded sensor that cleaves and releases pathogenic components, priming termites for improved antimicrobial defense. By means of rational design, we present an inexpensive, nontoxic small molecule glycomimetic that blocks tGNBP-2, thus exposing termites in vivo to accelerated infection and death from specific and opportunistic pathogens. Such a molecule, introduced into building materials and agricultural methods, could protect valuable assets from insect pests.

Purification and characterisation of endo-β-1,4-glucanase and laminarinase enzymes from the gecarcinid land crab Gecarcoidea natalis and the aquatic crayfish Cherax destructor

Laminarinase and endo-β-1,4-glucanase were purified and characterised from the midgut gland of the herbivorous land crab Gecarcoidea natalis and the crayfish Cherax destructor. The laminarinase isolated from G. natalis was estimated to have a molecular mass of 41 kDa by SDS-PAGE and 71 kDa by gel filtration chromatography. A similar discrepancy was noted for C. destructor. Possible reasons for this are discussed. Laminarinase (EC 3.2.1.6) from G. natalis had a Vmax of 42.0 μmol reducing sugars produced min–1 mg protein–1, a Kmof 0.126% (w/v) and an optimum pH range of 5.5–7, and hydrolysed mainlyβ-1,3-glycosidic bonds. In addition to the hydrolysis ofβ-1,3-glycosidic bonds, laminarinase (EC 3.2.1.39) from C. destructor was capable of significant hydrolysis of β-1,4-glycosidic bonds. It had a Vmax of 19.6 μmol reducing sugars produced min–1 mg protein–1, a Km of 0.059% (w/v) and an optimum pH of 5.5. Laminarinase from both species produced glucose and other short oligomers from the hydrolysis of laminarin. Endo-β-1,4-glucanase (EC 3.2.1.4) from G. natalis had a molecular mass of 52 kDa and an optimum pH of 4–7. It mainly hydrolysed β-1,4-glycosidic bonds, but was also capable of significant hydrolysis of β-1,3-glycosidic bonds. Two endo-β-1,4-glucanases, termed 1 and 2, with respective molecular masses of 53±3 and 52 kDa, were purified from C. destructor. Endo-β-1,4-glucanase 1 was only capable of hydrolysingβ-1,4-glycosidic bonds and had an optimum pH of 5.5. Endo-β-1,4-glucanases from both species produced some glucose, cellobiose and other short oligomers from the hydrolysis of carboxymethyl cellulose.

The interplay of processivity, substrate inhibition and a secondary substrate binding site of an insect exo-β-1,3-glucanase

Abracris flavolineata midgut contains a processive exo-beta-glucanase (ALAM) with lytic activity against Saccharomyces cerevisiae, which was purified (yield, 18%; enrichment, 37 fold; specific activity, 1.89 U/mg). ALAM hydrolyses fungal cells or callose from the diet. ALAM (45 kDa; pI 5.5; pH optimum 6) major products with 0.6 mM laminarin as substrate are beta-glucose (61%) and laminaribiose (39%). Kinetic data obtained with laminaridextrins and methylumbelliferyl glucoside suggest that ALAM has an active site with at least six subsites. The best fitting of kinetic data to theoretical curves is obtained using a model where one laminarin molecule binds first to a high-affinity accessory site, causing active site exposure, followed by the transference of the substrate to the active site. The two-binding-site model is supported by results from chemical modifications of amino acid residues and by ALAM action in MUbetaGlu plus laminarin. Low laminarin concentrations increase the modification of His, Tyr and Asp or Glu residues and MUbetaGlu hydrolysis, whereas high concentrations abolish modification and inhibit MUbetaGlu hydrolysis. Our data indicate that processivity results from consecutive transferences of substrate between accessory and active site and that substrate inhibition arises when both sites are occupied by substrate molecules abolishing processivity.

Proteinase, amylase, and proteinase-inhibitor activities in the gut of six cockroach species

Representative species, two from each of the cockroach families Blattidae, Blattellidae, and Blaberidae, have similar morphology of the digestive tract but differ in the physiology of digestion. The pH of crop and along the midgut varies in different species from 5.9 to 9.0 and the redox parameter from 10.1 to 12.9. Activities of proteinases and amylases in comparable gut regions differ among the species up to 100 times. Proteolytic activity is high in the midgut and moderate in the crop of Blattidae; in the other species, it is very low in the crop and increases to a moderate level in the posterior half of midgut (PM). The level of amylolytic activity is similar in the examined gut compartments of Blattidae and Blattellidae but low in the PM of Blaberidae. Blaberidae are also characterized by a high potential of the salivary glands, crop, and midgut to inhibit subtilisin, trypsin, and chymotrypsin. Inhibition of these proteinases by the extracts of salivary glands and gut is several orders of magnitude lower and often undetectable in the representatives of Blattidae and Blattellidae.

Potential role for gut microbiota in cell wall digestion and glucoside detoxification in Tenebrio molitor larvae

Tenebrio molitor larvae were successfully reared free of cultivatable gut lumen bacteria, yeasts and fungi using two approaches; aseptic rearing from surface sterilized eggs and by feeding larvae with antibiotic-containing food. Insects were reared on a rich-nutrient complete diet or a nutrient-poor refractory diet. A comparison of digestive enzyme activities in germ free and conventional insects containing a gut microbiota did not reveal gross differences in enzymes that degrade cell walls from bacteria (lysozyme), fungi (chitinase and laminarinase) and plants (cellulase and licheninase). This suggested that microbial-derived enzymes are not an essential component of the digestive process in this insect. However, more detailed analysis of T. molitor midgut proteins using an electrophoretic separation approach showed that some digestive enzymes were absent and others were newly expressed in microbiota-free larvae. Larvae reared in antibiotic-containing refractory wheat bran diet performed poorly in comparison with controls. The addition of saligenin, the aglycone of the plant glucoside salicin, has more deleterious effects on microbiota-free larvae than on the conventionally reared larvae, suggesting a detoxifying role of midgut microbiota. Analysis of the volatile organic compounds released from the faecal pellets of the larvae shows key differences in the profiles from conventionally reared and aseptically reared larvae. Pentadecene is a semiochemical commonly found in other beetle species. Here we demonstrate the absence of pentadecene from aseptically reared larvae in contrast to its presence in conventionally reared larvae. The results are discussed in the light of the hypothesis that microbial products play subtle roles in the life of the insect, they are involved in the digestion of refractory food, detoxification of secondary plant compounds and modify the volatile profiles of the insect host.

Cell-lytic activity of tobacco BY-2 induced by a fungal elicitor from alternaria alternata attributed to the expression of a class I beta-1,3-glucanase gene

Stress-induced cell-lytic activity was found in tobacco BY-2 cells treated with various stresses. Among 14 stresses, an elicitor fraction isolated from Alternaria alternata showed the highest inducing activity. Cell-lytic activity increased for 72 h even in the control sample, treated with distilled water, and several isozymes of beta-1,3-glucanases and chitinases were found to be involved in it. In contrast, cell-lytic activity in BY-2 cells treated with a fungal elicitor reached a higher level after 60 h. The principal enzymes specifically involved in this stress-induced portion are speculated to be basic beta-1,3-glucanases. A class I beta-1,3-glucanase gene (glu1) was found to be the specific gene for the stress-induced cell-lytic activity. Its expression became observable at 24 h, and the intensity reached a maximum at about 60-72 h. The glu1 was thus assigned as a late gene. Its role in the stress response is discussed in conjunction with earlier genes such as chitinases.