Molecular cloning, expression, and enzymatic activity of a novel endogenous cellulase from the mulberry longicorn beetle, Apriona germari

Deciphering the complex interplay between gut microbiota and crop residue breakdown in forager and hive bees (Apis mellifera L.)

This study investigates A. mellifera gut microbiota diversity and enzymatic activities, aiming to utilize identified isolates for practical applications in sustainable crop residue management and soil health enhancement. This study sampled honey bees, analyzed gut bacterial diversity via 16S rRNA gene, and screened isolates for cellulolytic, hemicellulolytic, and pectinolytic activities, with subsequent assessment of enzymatic potential. The study reveals that cellulolytic and hemicellulolytic bacterial isolates, mainly from γ-Proteobacteria, Actinobacteria, and Firmicutes, have significant potential for crop residue management. Some genera, like Aneurinibacillus, Bacillus, Clostridium, Enterobacter, Serratia, Stenotrophomonas, Apilactobacillus, Lysinibacillus, and Pseudomonas, are very good at breaking down cellulose and hemicellulase. Notable cellulose-degrading genera include Cedecea (1.390 ± 0.57), Clostridium (1.360 ± 0.86 U/mg), Enterobacter (1.493 ± 1.10 U/mg), Klebsiella (1.380 ± 2.03 U/mg), and Serratia (1.402 ± 0.31 U/mg), while Aneurinibacillus (1.213 ± 1.12 U/mg), Bacillus (3.119 ± 0.55 U/mg), Enterobacter (1.042 ± 0.14 U/mg), Serratia (1.589 ± 0.05 U/mg), and Xanthomonas (1.156 ± 0.08 U/mg) excel in hemicellulase activity. Specific isolates with high cellulolytic and hemicellulolytic activities are identified, highlighting their potential for crop residue management. The research explores gut bacterial compartmentalization in A. mellifera, emphasising gut physiology's role in cellulose and hemicellulose digestion. Pectinolytic activity is observed, particularly in the Bacillaceae clade (3.229 ± 0.02), contributing to understanding the honey bee gut microbiome. The findings offer insights into microbiome diversity and enzymatic capabilities, with implications for biotechnological applications in sustainable crop residue management. The study concludes by emphasizing the need for ongoing research to uncover underlying mechanisms and ecological factors influencing gut microbiota, impacting honey bee health, colony dynamics, and advancements in crop residue management.

Characterization of bacterial diversity and screening of cellulose-degrading bacteria in the gut system of Glenea cantor (Fabricius) larvae

The intestinal bacteria of longhorn beetles would be ideal targets for pest control and lignocellulosic resources by destroying or exploiting their cellulose-degrading function. This article aims to investigate the diversity and community structure of intestinal bacteria the oligophagous longhorn beetle Glenea cantor. Additionally, it seeks to identify the presence of lignocellulose-degrading bacteria in the gut, and explore their role in consuming host kapok trees Bombax malabaricum. In this study, the bacterial community from G. cantor was examined by Illumina sequencing of 16S ribosomal RNA (rRNA) targeting the V3 and V4 regions. A total of 563,201 valid sequences and 814 OTUs were obtained. The dominant phyla were Proteobacteria, and the dominant genera were Acinetobacter and Lactococcus. The analysis of microbial diversity revealed a high bacterial diversity in the samples, with the gut bacteria playing a crucial role in the physiological activities of the host, particularly, 9 genera of intestinal bacteria with cellulose degradation function were found, highlighting their vital role in cellulose degradation. Five strains of cellulose-degrading bacteria, belonging to the genus Pseudomonas, were obtained from the intestinal tract of G. cantor larvae using traditional isolation and culture techniques as well as 16S rDNA sequencing. Among these strains, A4 exhibited a cellulase activity of 94.42 ± 0.42 U/mL, while A5 displayed the highest filter paper enzyme activity of 127.46 ± 3.54 U/mL. These results offered valuable insights into potential targets for pest control through internal attack digestion and cellulose-degrading bacteria in longhorn beetles.

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.

Duplication of horizontally acquired GH5_2 enzymes played a central role in the evolution of longhorned beetles

The rise of functional diversity through gene duplication contributed to the adaption of organisms to various environments. Here we investigate the evolution of putative cellulases of the subfamily 2 of glycoside hydrolase family 5 (GH5_2) in the Cerambycidae (longhorned beetles), a megadiverse assemblage of mostly xylophagous beetles. Cerambycidae originally acquired GH5_2 from a bacterial donor through horizontal gene transfer (HGT), and extant species harbor multiple copies that arose from gene duplication. We ask how these digestive enzymes contributed to the ability of these beetles to feed on wood. We analyzed 113 GH5_2, including the functional characterization of 52 of them, derived from 25 species covering most subfamilies of Cerambycidae. Ancestral gene duplications led to five well-defined groups with distinct substrate specificity, allowing these beetles to break down, in addition to cellulose, polysaccharides that are abundant in plant cell walls (PCWs), namely, xyloglucan, xylan, and mannans. Resurrecting the ancestral enzyme originally acquired by HGT, we show it was a cellulase that was able to break down glucomannan and xylan. Finally, recent gene duplications further expanded the catalytic repertoire of cerambycid GH5_2, giving rise to enzymes that favor transglycosylation over hydrolysis. We suggest that HGT and gene duplication, which shaped the evolution of GH5_2, played a central role in the ability of cerambycid beetles to use a PCW-rich diet and may have contributed to their successful radiation.

Analyzing the Substrate Specificity of a Class of Long-Horned-Beetle-Derived Xylanases by Using Synthetic Arabinoxylan Oligo- and Polysaccharides

Xylophagous long-horned beetles thrive in challenging environments. To access nutrients, they secrete plant-cell-wall-degrading enzymes in their gut fluid; among them are cellulases of the subfamily 2 of glycoside hydrolase family 5 (GH5_2). Recently, we discovered that several beetle-derived GH5_2s use xylan as a substrate instead of cellulose, which is unusual for this family of enzymes. Here, we analyze the substrate specificity of a GH5_2 xylanase from the beetle Apriona japonica (AJAGH5_2-1) using commercially available substrates and synthetic arabinoxylan oligo- and polysaccharides. We demonstrate that AJAGH5_2-1 processes arabinoxylan polysaccharides in a manner distinct from classical xylanase families such as GH10 and GH11. AJAGH5_2-1 is active on long oligosaccharides and cleaves at the non-reducing end of a substituted xylose residue (position +1) only if: 1) three xylose residues are present upstream and downstream of the cleavage site, and 2) xylose residues at positions -1, -2, +2 and +3 are not substituted.

Evolution and functional characterization of CAZymes belonging to subfamily 10 of glycoside hydrolase family 5 (GH5_10) in two species of phytophagous beetles

Hemicelluloses, such as xyloglucan, xylan and mannans, consist of a heterogeneous array of plant-derived polysaccharides that form the plant cell wall. These polysaccharides differ from each other in their structure and physiochemical properties, but they share a β-(1,4)-linked sugar backbone. Hemicelluloses can be hydrolyzed by plant-cell-wall-degrading enzymes (PCWDEs), which are widely distributed in phytopathogenic microbes. Recently, it has become apparent that phytophagous beetles also produce their own PCWDEs. Our previous work identified genes encoding putative mannanases belonging to the subfamily 10 of glycoside hydrolase (GH) family 5 (GH5_10) in the genomes of the leaf beetle, Gastrophysa viridula (Chrysomelidae, Chrysomelinae; one gene), and of the bean beetle, Callosobruchus maculatus (Chrysomelidae, Bruchinae; four genes). In contrast to proteins from other GH5 subfamilies, GH5_10 proteins are patchily distributed within the tree of life and have so far hardly been investigated. We addressed the following questions: Are beetle-derived GH5_10s active PCWDEs? How did they evolve? What is their physiological function? Using heterologous protein expression and enzymatic assays, we show that the G. viridula GH5_10 protein is an endo-β-1,4-mannanase. We also demonstrate that only one out of four C. maculatus GH5_10 proteins is an endo-β-1,4-mannanase, which has additional activity on carboxymethyl cellulose. Unexpectedly, another C. maculatus GH5_10 protein has evolved to use xylan instead of mannans as a substrate. RNAi experiments in G. viridula indicate (i) that the sole GH5_10 protein is responsible for breaking down mannans in the gut and (ii) that this breakdown may rather be accessory and may facilitate access to plant cell content, which is rich in nitrogen and simple sugars. Phylogenetic analyses indicate that coleopteran-derived GH5_10 proteins cluster together with Chelicerata-derived ones. Interestingly, other insect-derived GH5_10 proteins cluster elsewhere, suggesting insects have several independent evolutionary origins.

Transgenic Plant-Produced Hydrolytic Enzymes and the Potential of Insect Gut-Derived Hydrolases for Biofuels

Various perennial C4 grass species have tremendous potential for use as lignocellulosic biofuel feedstocks. Currently available grasses require costly pre-treatment and exogenous hydrolytic enzyme application to break down complex cell wall polymers into sugars that can then be fermented into ethanol. It has long been hypothesized that engineered feedstock production of cell wall degrading (CWD) enzymes would be an efficient production platform for of exogenous hydrolytic enzymes. Most research has focused on plant overexpression of CWD enzyme-coding genes from free-living bacteria and fungi that naturally break down plant cell walls. Recently, it has been found that insect digestive tracts harbor novel sources of lignocellulolytic biocatalysts that might be exploited for biofuel production. These CWD enzyme genes can be located in the insect genomes or in symbiotic microbes. When CWD genes are transformed into plants, negative pleiotropic effects are possible such as unintended cell wall digestion. The use of codon optimization along with organelle and tissue specific targeting improves CWD enzyme yields. The literature teaches several important lessons on strategic deployment of CWD genes in transgenic plants, which is the focus of this review.

Proteome Analysis of Watery Saliva Secreted by Green Rice Leafhopper, Nephotettix cincticeps

The green rice leafhopper, Nephotettix cincticeps, is a vascular bundle feeder that discharges watery and gelling saliva during the feeding process. To understand the potential functions of saliva for successful and safe feeding on host plants, we analyzed the complexity of proteinaceous components in the watery saliva of N. cincticeps. Salivary proteins were collected from a sucrose diet that adult leafhoppers had fed on through a membrane of stretched parafilm. Protein concentrates were separated using SDS-PAGE under reducing and non-reducing conditions. Six proteins were identified by a gas-phase protein sequencer and two proteins were identified using LC-MS/MS analysis with reference to expressed sequence tag (EST) databases of this species. Full -length cDNAs encoding these major proteins were obtained by rapid amplification of cDNA ends-PCR (RACE-PCR) and degenerate PCR. Furthermore, gel-free proteome analysis that was performed to cover the broad range of salivary proteins with reference to the latest RNA-sequencing data from the salivary gland of N. cincticeps, yielded 63 additional protein species. Out of 71 novel proteins identified from the watery saliva, about 60 % of those were enzymes or other functional proteins, including GH5 cellulase, transferrin, carbonic anhydrases, aminopeptidase, regucalcin, and apolipoprotein. The remaining proteins appeared to be unique and species- specific. This is the first study to identify and characterize the proteins in watery saliva of Auchenorrhyncha species, especially sheath-producing, vascular bundle-feeders.

Characterization of cellulolytic activity in the gut of the terrestrial land slug Arion ater: Biochemical identification of targets for intensive study

The level of cellulolytic activity in different areas of the gut of the terrestrial slug Arion ater was assayed at different temperatures and pH values. To do this, crude gut proteins were isolated and assayed using modified dinitrosalicylic acid reducing sugar assay. Crude protein samples were also separated and cellulolytic activity identified using in gel CMC zymography and esculin hydrate activity gel assays. pH and temperature profiling revealed optimum cellulolytic activity between pH5.0 and 6.0 for different gut regions and retention of up to 90% of activity at temperatures up to 50°C. Zymograms and activity gels revealed multiple endoglucanase and β-glucosidase enzymes. To further investigate the source of this cellulolytic activity bacterial isolates from the gut were tested for endoglucanase and β-glucosidase activity using growth plate assays. 12 cellulolytic microbes were identified using 16S rDNA gene sequencing. These include members of the genera Buttiauxella, Enterobacter, Citrobacter, Serratia and Klebsiella. Gut metagenomic DNA was then subjected to PCR, targeting a 400bp region of the 16SrDNA gene which was subsequently separated and individuals identified using DGGE. This identified members of the genera Citrobacter, Serratia, Pectobacterium, Acinetobacter, Mycoplasma, Pantoea and Erwinia. In summary, multiple glycoside hydrolase enzymes active over a broad range of temperature and pH values in a relatively under studied organism were detected, indicating that the gut of A. ater is a viable target for intensive study to identify novel carbohydrate active enzymes that may be used in the biofuel industry.

Identification and characterization of plant cell wall degrading enzymes from three glycoside hydrolase families in the cerambycid beetle Apriona japonica

Xylophagous insects have evolved to thrive in a highly challenging environment. For example, wood-boring beetles from the family Cerambycidae feed exclusively on woody tissues, and to efficiently access the nutrients present in this sub-optimal environment, they have to cope with the lignocellulose barrier. Whereas microbes of the insect's gut flora were hypothesized to be responsible for the degradation of lignin, the beetle itself depends heavily on the secretion of a range of enzymes, known as plant cell wall degrading enzymes (PCWDEs), to efficiently digest both hemicellulose and cellulose networks. Here we sequenced the larval gut transcriptome of the Mulberry longhorn beetle, Apriona japonica (Cerambycidae, Lamiinae), in order to investigate the arsenal of putative PCWDEs secreted by this species. We combined our transcriptome with all available sequencing data derived from other cerambycid beetles in order to analyze and get insight into the evolutionary history of the corresponding gene families. Finally, we heterologously expressed and functionally characterized the A. japonica PCWDEs we identified from the transcriptome. Together with a range of endo-β-1,4-glucanases, we describe here for the first time the presence in a species of Cerambycidae of (i) a xylanase member of the subfamily 2 of glycoside hydrolase family 5 (GH5 subfamily 2), as well as (ii) an exopolygalacturonase from family GH28. Our analyses greatly contribute to a better understanding of the digestion physiology of this important group of insects, many of which are major pests of forestry worldwide.

Cellulases from insects

Bioethanol is currently produced by the fermentation of sugary and starchy crops, but waste plant biomass is a more abundant source because sugars can be derived directly from cellulose. One of the limiting steps in the biomass-to-ethanol process is the degradation of cellulose to fermentable sugars (saccharification). This currently relies on the use of bacterial and/or fungal cellulases, which tend to have low activity under biorefinery conditions and are easily inhibited. Some insect species feed on plant biomass and can efficiently degrade cellulose to produce glucose as an energy source. Although insects were initially thought to require symbiotic relationships with bacteria and fungi to break down cellulose, several species in the orders Dictyoptera, Orthoptera, and Coleoptera have now been shown to produce their own cellulases in the midgut or salivary glands, and putative cellulase genes have been identified in other orders. Insect cellulases often work in concert with cellulases provided by symbiotic microbiota in the gut to achieve efficient cellulolysis. We discuss the current status of insect cellulases and potential strategies that could be used to find novel enzymes and improve their efficiency.

Transcriptome analysis of the salivary glands of potato leafhopper, Empoasca fabae

The potato leafhopper, Empoasca fabae, is a pest of economic crops in the United States and Canada, where it causes damage known as hopperburn. Saliva, along with mechanical injury, leads to decreases in gas exchange rates, stunting and chlorosis. Although E. fabae saliva is known to induce plant responses, little knowledge exists of saliva composition at the molecular level. We subjected the salivary glands of E. fabae to Roche 454-pyrosequencing which resulted significant number (30,893) of expressed sequence tags including 2805 contigs and 28,088 singletons. A high number of sequences (78%) showed similarity to other insect species in GenBank, including Triboliumcastaneum, Drosophilamelanogaster and Acrythosiphonpisum. KEGG analysis predicted the presence of pathways for purine and thiamine metabolic, biosynthesis of secondary metabolites, drug metabolism, and lysine degradation. Pfam analysis showed a high number of cellulase and carboxylesterase protein domains. Expression analysis of candidate genes (alpha amylase, lipase, pectin lyase, etc.) among different tissues revealed tissue-specific expression of digestive enzymes in E. fabae. This is the first study to characterize the sialotranscriptome of E. fabae and the first for any species in the family of Cicadellidae. Due to the status of these insects as economic pests, knowledge of which genes are active in the salivary glands is important for understanding their impact on host plants.

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.

Molecular cloning and functional characterization of an endogenous endoglucanase belonging to GHF45 from the western corn rootworm, Diabrotica virgifera virgifera

A novel insect β-1,4-endoglucanase (DvvENGaseI) gene belonging to the glycoside hydrolase family (GHF) 45 was identified from the western corn rootworm, Diabrotica virgifera virgifera. The cDNA of the DvvENGaseI consisted of a 720 bp open reading frame encoding a 239 amino-acid protein. Analysis of the amino acid sequence revealed that DvvENGaseI exhibits 60% protein sequence identity when compared with an endoglucanase belonging to GHF45 from another beetle, Leptinotarsa decemlineata. Western blot analyses using a polyclonal antiserum developed from a partial peptide sequence revealed that DvvENGaseI expression coincided with body regions corresponding to the fore-, mid- and hindgut, although regions corresponding to the midgut and hindgut were the primary sites for DvvENGaseI expression. Functional analysis of the DvvENGaseI by RNA interference (RNAi) indicated that nearly complete knock-down of gene expression could be obtained by injection of dsRNA based on qRT-PCR and western blot analysis. However, suppression only resulted in slight developmental delays suggesting that this gene may be part of a larger system of cellulose degrading enzymes.

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.

Expression of Trichoderma viride endoglucanase III in the larvae of silkworm, Bombyx mori L. and characteristic analysis of the recombinant protein

Endoglucanase is a part of cellulase which hydrolyzes cellulose into glucose. In this study, we cloned endoglucanase III (EG III) gene from Trichoderma viride strain AS 3.3711 using a PCR-based exon splicing method, and expressed EG III recombinant protein in both silkworm BmN cell line and silkworm larvae with an improved Bac-to-Bac/BmNPV mutant baculovirus expression system, which lacks the chiA and v-cath genes of Bombyx mori nucleopolyhedrovirus (BmNPV). The result showed that around 45 kDa protein was visualized in BmN cells at 48 h after the second generation recombinant mBacmid/BmNPV/EG III baculovirus infection. The enzymes from recombinant baculoviruses infected silkworms exhibited significant maximum enzyme activity at the environmental condition of pH 8.0 and temperature 50°C, and increased 20.94 and 19.13% compared with that from blank mBacmid/BmNPV baculoviruses infected silkworms and normal silkworms, respectively. It was stable at pH range from 5.0 to 9.0 and at temperature range from 40 to 60°C. It provided a possibility to generate transgenic silkworms expressing bio-active cellulase, which can catabolize dietary fibers more efficiently, and it might be of great significance for sericulture industry.

Multiple lateral gene transfers and duplications have promoted plant parasitism ability in nematodes

Lateral gene transfer from prokaryotes to animals is poorly understood, and the scarce documented examples generally concern genes of uncharacterized role in the receiver organism. In contrast, in plant-parasitic nematodes, several genes, usually not found in animals and similar to bacterial homologs, play essential roles for successful parasitism. Many of these encode plant cell wall-degrading enzymes that constitute an unprecedented arsenal in animals in terms of both abundance and diversity. Here we report that independent lateral gene transfers from different bacteria, followed by gene duplications and early gain of introns, have shaped this repertoire. We also show protein immunolocalization data that suggest additional roles for some of these cell wall-degrading enzymes in the late stages of these parasites' life cycle. Multiple functional acquisitions of exogenous genes that provide selective advantage were probably crucial for the emergence and proficiency of plant parasitism in nematodes.

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

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

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.

Cellulolytic systems in insects

Despite the presence of many carbohydrolytic activities in insects, their cellulolytic mechanisms are poorly understood. Whereas cellulase genes are absent from the genomes of Drosophila melanogaster or Bombyx mori, other insects such as termites produce their own cellulases. Recent studies using molecular biological techniques have brought new insights into the mechanisms by which the insects and their microbial symbionts digest cellulose in the small intestine. DNA sequences of cellulase and associated genes, as well as physiological and morphological information about the digestive systems of cellulase-producing insects, may allow the efficient use of cellulosic biomass as a sustainable energy source.

The genomes of root-knot nematodes

Plant-parasitic nematodes are the most destructive group of plant pathogens worldwide and are extremely challenging to control. The recent completion of two root-knot nematode genomes opens the way for a comparative genomics approach to elucidate the success of these parasites. Sequencing revealed that Meloidogyne hapla, a diploid that reproduces by facultative, meiotic parthenogenesis, encodes approximately 14,200 genes in a compact, 54 Mpb genome. Indeed, this is the smallest metazoan genome completed to date. By contrast, the 86 Mbp Meloidogyne incognita genome encodes approximately 19,200 genes. This species reproduces by obligate mitotic parthenogenesis and exhibits a complex pattern of aneuploidy. The genome includes triplicated regions and contains allelic pairs with exceptionally high degrees of sequence divergence, presumably reflecting adaptations to the strictly asexual reproductive mode. Both root-knot nematode genomes have compacted gene families compared with the free-living nematode Caenorhabditis elegans, and both encode large suites of enzymes that uniquely target the host plant. Acquisition of these genes, apparently via horizontal gene transfer, and their subsequent expansion and diversification point to the evolutionary history of these parasites. It also suggests new routes to their control.

Evolution of GHF5 endoglucanase gene structure in plant-parasitic nematodes: no evidence for an early domain shuffling event

Background

Endo-1,4-beta-glucanases or cellulases from the glycosyl hydrolase family 5 (GHF5) have been found in numerous bacteria and fungi, and recently also in higher eukaryotes, particularly in plant-parasitic nematodes (PPN). The origin of these genes has been attributed to horizontal gene transfer from bacteria, although there still is a lot of uncertainty about the origin and structure of the ancestral GHF5 PPN endoglucanase. It is not clear whether this ancestral endoglucanase consisted of the whole gene cassette, containing a catalytic domain and a carbohydrate-binding module (CBM, type 2 in PPN and bacteria) or only of the catalytic domain while the CBM2 was retrieved by domain shuffling later in evolution. Previous studies on the evolution of these genes have focused primarily on data of sedentary nematodes, while in this study, extra data from migratory nematodes were included.

Results

Two new endoglucanases from the migratory nematodes Pratylenchus coffeae and Ditylenchus africanus were included in this study. The latter one is the first gene isolated from a PPN of a different superfamily (Sphaerularioidea); all previously known nematode endoglucanases belong to the superfamily Tylenchoidea (order Rhabditida). Phylogenetic analyses were conducted with the PPN GHF5 endoglucanases and homologous endoglucanases from bacterial and other eukaryotic lineages such as beetles, fungi and plants. No statistical incongruence between the phylogenetic trees deduced from the catalytic domain and the CBM2 was found, which could suggest that both domains have evolved together. Furthermore, based on gene structure data, we inferred a model for the evolution of the GHF5 endoglucanase gene structure in plant-parasitic nematodes. Our data confirm a close relationship between Pratylenchus spp. and the root knot nematodes, while some Radopholus similis endoglucanases are more similar to cyst nematode genes.

Conclusion

We conclude that the ancestral PPN GHF5 endoglucanase gene most probably consisted of the whole gene cassette, i.e. the GHF5 catalytic domain and the CBM2, rather than that it evolved by domain shuffling. Our evolutionary model for the gene structure in PPN GHF5 endoglucanases implies the occurrence of an early duplication event, and more recent gene duplications at genus or species level.

Genome sequence of the metazoan plant-parasitic nematode Meloidogyne incognita

Plant-parasitic nematodes are major agricultural pests worldwide and novel approaches to control them are sorely needed. We report the draft genome sequence of the root-knot nematode Meloidogyne incognita, a biotrophic parasite of many crops, including tomato, cotton and coffee. Most of the assembled sequence of this asexually reproducing nematode, totaling 86 Mb, exists in pairs of homologous but divergent segments. This suggests that ancient allelic regions in M. incognita are evolving toward effective haploidy, permitting new mechanisms of adaptation. The number and diversity of plant cell wall-degrading enzymes in M. incognita is unprecedented in any animal for which a genome sequence is available, and may derive from multiple horizontal gene transfers from bacterial sources. Our results provide insights into the adaptations required by metazoans to successfully parasitize immunocompetent plants, and open the way for discovering new antiparasitic strategies.

Expression and characterization of two secreted His6-tagged endo-beta-1,4-glucanases from the mollusc Ampullaria crossean in Pichia pastoris

Two endo-beta-1,4-glucanase cDNAs, eg27I and eg27II, from the mollusc Ampullaria crossean were expressed in Pichia pastoris cells. The secreted His6-tagged proteins were purified in a single chromatography step. The purified recombinant EG27I and EG27II showed enzymatic activity on carboxylmethyl cellulose sodium salt at 15.31 U/mg and 12.40 U/mg, respectively. The optimum pH levels of the recombinant EG27I and EG27II were 5.5 and 5.5-6.0, respectively, and the optimum temperatures were 50 degrees C and 50 degrees C-55 degrees C, respectively. The pH stability study revealed that both EG27I and EG27II showed their highest stability at pH 8.0. Analysis of their thermostability indicated that both EG27I and EG27II were relatively stable up to 40 degrees C. Site-directed mutagenesis of Asp43 and Asp153 of both EG27I and EG27II showed that the two Asp residues are critical for the enzymatic activity.