Bacterial chitinases: properties and potential

Characterization of regulatory regions involved in the inducible expression of chiB in Bacillus thuringiensis

Expression of the chiB gene from Bacillus thuringiensis Bti75 was defined as inducible by the use of transcriptional fusions with the bgaB reporter gene. The transcription start site of the chiB gene was identified as the C base located 132 base pairs upstream of the start codon. Analysis of 5' and 3' deletions of the chiB promoter region revealed that the sequence from position -192 to +36 with respect to the transcription start site was necessary for wild-type levels of inducible expression of the chiB gene. The minimal promoter region for the expression of chiB gene was identified as the sequence from position -100 to +12. Furthermore, a 16-bp sequence (designated dre) downstream of the minimal promoter region of chiB was shown to be required for chitin induction. To confirm the function of this 16-bp sequence, 25 base substitutions were introduced into the dre site. Most of the mutations resulted in constitutive expression, or the efficiency of induction decreased. All mutations identified the dre sequence as a critical site for the inducible expression of chiB. In addition, the dre site was shown to interact with a sequence-specific DNA binding factor of strain Bti75 cultured in the absence of the inducer.

An ammonium sulfate sensitive chitinase from Streptomyces sp. CS501

A chitinase from Streptomyces sp. CS501 was isolated from the Korean soil sample, purified by single-step chromatography, and biochemically characterized. The extracellular chitinase (Ch501) was purified to 4.60 fold with yield of 28.74 % using Sepharose Cl-6B column. The molecular mass of Ch501 was approximately 43 kDa as estimated by SDS-PAGE and zymography. The enzyme (Ch501) was found to be stable over a broad pH range (5.0-10.0) and temperature (up to 50 °C), and have an optimum temperature of 60 °C. N-terminal sequence of Ch501 was AAYDDAAAAA. Intriguingly, Ch501 was highly sensitive to ammonium sulfate but it's completely suppressed activity was recovered after desalting out. TLC analysis of Ch501 showed the production of N-acetyl D-glucosamine (GlcNAc) and Diacetylchitobiose (GlcNAc)2, as a principal hydrolyzed product. Ch501 shows antifungal activity against Fusarium solani and Aspergillus brasiliensis, which can be used for the biological control of fungus. As has been simple in purification, stable in a broad range of pH, ability to produce oligosaccharides, and antifungal activity showed that Ch501 has potential applications in industries as for chitooligosaccharides production used as prebiotics and/or for the biological control of plant pathogens in agriculture.

Bacterial chitinase with phytopathogen control capacity from suppressive soil revealed by functional metagenomics

Plant disease caused by fungal pathogens results in vast crop damage globally. Microbial communities of soil that is suppressive to fungal crop disease provide a source for the identification of novel enzymes functioning as bioshields against plant pathogens. In this study, we targeted chitin-degrading enzymes of the uncultured bacterial community through a functional metagenomics approach, using a fosmid library of a suppressive soil metagenome. We identified a novel bacterial chitinase, Chi18H8, with antifungal activity against several important crop pathogens. Sequence analyses show that the chi18H8 gene encodes a 425-amino acid protein of 46 kDa with an N-terminal signal peptide, a catalytic domain with the conserved active site F¹⁷⁵DGIDIDWE¹⁸³, and a chitinase insertion domain. Chi18H8 was expressed (pGEX-6P-3 vector) in Escherichia coli and purified. Enzyme characterization shows that Chi18H8 has a prevalent chitobiosidase activity with a maximum activity at 35 °C at pH lower than 6, suggesting a role as exochitinase on native chitin. To our knowledge, Chi18H8 is the first chitinase isolated from a metagenome library obtained in pure form and which has the potential to be used as a candidate agent for controlling fungal crop diseases. Furthermore, Chi18H8 may also answer to the demand for novel chitin-degrading enzymes for a broad range of other industrial processes and medical purposes.

Paenibacillus larvae chitin-degrading protein PlCBP49 is a key virulence factor in American Foulbrood of honey bees

Paenibacillus larvae, the etiological agent of the globally occurring epizootic American Foulbrood (AFB) of honey bees, causes intestinal infections in honey bee larvae which develop into systemic infections inevitably leading to larval death. Massive brood mortality might eventually lead to collapse of the entire colony. Molecular mechanisms of host-microbe interactions in this system and of differences in virulence between P. larvae genotypes are poorly understood. Recently, it was demonstrated that the degradation of the peritrophic matrix lining the midgut epithelium is a key step in pathogenesis of P. larvae infections. Here, we present the isolation and identification of PlCBP49, a modular, chitin-degrading protein of P. larvae and demonstrate that this enzyme is crucial for the degradation of the larval peritrophic matrix during infection. PlCBP49 contains a module belonging to the auxiliary activity 10 (AA10, formerly CBM33) family of lytic polysaccharide monooxygenases (LPMOs) which are able to degrade recalcitrant polysaccharides. Using chitin-affinity purified PlCBP49, we provide evidence that PlCBP49 degrades chitin via a metal ion-dependent, oxidative mechanism, as already described for members of the AA10 family. Using P. larvae mutants lacking PlCBP49 expression, we analyzed in vivo biological functions of PlCBP49. In the absence of PlCBP49 expression, peritrophic matrix degradation was markedly reduced and P. larvae virulence was nearly abolished. This indicated that PlCBP49 is a key virulence factor for the species P. larvae. The identification of the functional role of PlCBP49 in AFB pathogenesis broadens our understanding of this important family of chitin-binding and -degrading proteins, especially in those bacteria that can also act as entomopathogens.

Small RNA functions in carbon metabolism and virulence of enteric pathogens

Enteric pathogens often cycle between virulent and saprophytic lifestyles. To endure these frequent changes in nutrient availability and composition bacteria possess an arsenal of regulatory and metabolic genes allowing rapid adaptation and high flexibility. While numerous proteins have been characterized with regard to metabolic control in pathogenic bacteria, small non-coding RNAs have emerged as additional regulators of metabolism. Recent advances in sequencing technology have vastly increased the number of candidate regulatory RNAs and several of them have been found to act at the interface of bacterial metabolism and virulence factor expression. Importantly, studying these riboregulators has not only provided insight into their metabolic control functions but also revealed new mechanisms of post-transcriptional gene control. This review will focus on the recent advances in this area of host-microbe interaction and discuss how regulatory small RNAs may help coordinate metabolism and virulence of enteric pathogens.

Interaction of di-N-acetylchitobiosyl moranoline with a family GH19 chitinase from moss, Bryum coronatum

Tri-N-acetylchitotriosyl moranoline, (GlcNAc)3-M, was previously shown to strongly inhibit lysozyme (Ogata M, Umemoto N, Ohnuma T, Numata T, Suzuki A, Usui T, Fukamizo T. 2013. A novel transition-state analogue for lysozyme, 4-O-β-tri-Nacetylchitotriosyl moranoline, provided evidence supporting the covalent glycosyl-enzyme intermediate. J Biol Chem. 288:6072-6082). The findings prompted us to examine the interaction of di-N-acetylchitobiosyl moranoline, (GlcNAc)2-M, with a family GH19 chitinase from moss, Bryum coronatum (BcChi19A). Thermal unfolding experiments using BcChi19A and the catalytic acid-deficient mutant (BcChi19A-E61A) revealed that the transition temperature (Tm) was elevated by 4.3 and 5.8°C, respectively, upon the addition of (GlcNAc)2-M, while the chitin dimer, (GlcNAc)2, elevated Tm only by 1.0 and 1.4°C, respectively. By means of isothermal titration calorimetry, binding free energy changes for the interactions of (GlcNAc)3 and (GlcNAc)2-M with BcChi19A-E61A were determined to be -5.2 and -6.6 kcal/mol, respectively, while (GlcNAc)2 was found to interact with BcChi19A-E61A with markedly lower affinity. nuclear magnetic resonance titration experiments using (15)N-labeled BcChi19A and BcChi19A-E61A revealed that both (GlcNAc)2 and (GlcNAc)2-M interact with the region surrounding the catalytic center of the enzyme and that the interaction of (GlcNAc)2-M is markedly stronger than that of (GlcNAc)2 for both enzymes. However, (GlcNAc)2-M was found to moderately inhibit the hydrolytic reaction of chitin oligosaccharides catalyzed by BcChi19A (IC50 = 130-620 μM). A molecular dynamics simulation of BcChi19A in complex with (GlcNAc)2-M revealed that the complex is quite stable and the binding mode does not significantly change during the simulation. The moranoline moiety of (GlcNAc)2-M did not fit into the catalytic cleft (subsite -1) but was rather in contact with subsite +1. This situation may result in the moderate inhibition toward the BcChi19A-catalyzed hydrolysis.

Fungal lysis by a soil bacterium fermenting cellulose

Recycling of plant biomass by a community of bacteria and fungi is fundamental to carbon flow in terrestrial ecosystems. Here we report how the plant fermenting, soil bacterium Clostridium phytofermentans enhances growth on cellulose by simultaneously lysing and consuming model fungi from soil. We investigate the mechanism of fungal lysis to show that among the dozens of different glycoside hydrolases C. phytofermentans secretes on cellulose, the most highly expressed enzymes degrade fungi rather than plant substrates. These enzymes, the GH18 Cphy1799 and Cphy1800, synergize to hydrolyse chitin, a main component of the fungal cell wall. Purified enzymes inhibit fungal growth and mutants lacking either GH18 grow normally on cellulose and other plant substrates, but have a reduced ability to hydrolyse chitinous substrates and fungal hyphae. Thus, C. phytofermentans boosts growth on cellulose by lysing fungi with its most highly expressed hydrolases, highlighting the importance of fungal interactions to the ecology of cellulolytic bacteria.

Engineering of Corynebacterium glutamicum for growth and L-lysine and lycopene production from N-acetyl-glucosamine

Sustainable supply of feedstock has become a key issue in process development in microbial biotechnology. The workhorse of industrial amino acid production Corynebacterium glutamicum has been engineered towards utilization of alternative carbon sources. Utilization of the chitin-derived aminosugar N-acetyl-glucosamine (GlcNAc) for both cultivation and production with C. glutamicum has hitherto not been investigated. Albeit this organism harbors the enzymes N-acetylglucosamine-6-phosphatedeacetylase and glucosamine-6P deaminase of GlcNAc metabolism (encoded by nagA and nagB, respectively) growth of C. glutamicum with GlcNAc as substrate was not observed. This was attributed to the lack of a functional system for GlcNAc uptake. Of the 17 type strains of the genus Corynebacterium tested here for their ability to grow with GlcNAc, only Corynebacterium glycinophilum DSM45794 was able to utilize this substrate. Complementation studies with a GlcNAc-uptake deficient Escherichia coli strain revealed that C. glycinophilum possesses a nagE-encoded EII permease for GlcNAc uptake. Heterologous expression of the C. glycinophilum nagE in C. glutamicum indeed enabled uptake of GlcNAc. For efficient GlcNac utilization in C. glutamicum, improved expression of nagE with concurrent overexpression of the endogenous nagA and nagB genes was found to be necessary. Based on this strategy, C. glutamicum strains for the efficient production of the amino acid L-lysine as well as the carotenoid lycopene from GlcNAc as sole substrate were constructed.

Crystal structure of a "loopless" GH19 chitinase in complex with chitin tetrasaccharide spanning the catalytic center

DESCRIPTIONS

The structure of a GH19 chitinase from the moss Bryum coronatum (BcChi-A) in complex with the substrate was examined by X-ray crystallography and NMR spectroscopy in solution. The X-ray crystal structure of the inactive mutant of BcChi-A (BcChi-A-E61A) liganded with chitin tetramer (GlcNAc)4 revealed a clear electron density of the tetramer bound to subsites -2, -1, +1, and +2. Individual sugar residues were recognized by several amino acids at these subsites through a number of hydrogen bonds. This is the first crystal structure of GH19 chitinase liganded with oligosaccharide spanning the catalytic center. NMR titration experiments of chitin oligosaccharides into the BcChi-A-E61A solution showed that the binding mode observed in the crystal structure is similar to that in solution. The C-1 carbon of -1 GlcNAc, the Oε1 atom of the catalytic base (Glu70), and the Oγ atom of Ser102 form a "triangle" surrounding the catalytic water, and the arrangement structurally validated the proposed catalytic mechanism of GH19 chitinases. The glycosidic linkage between -1 and +1 sugars was found to be twisted and under strain. This situation may contribute to the reduction of activation energy for hydrolysis. The complex structure revealed a more refined mechanism of the chitinase catalysis.

An acidic, thermostable exochitinase with β-N-acetylglucosaminidase activity from Paenibacillus barengoltzii converting chitin to N-acetyl glucosamine

BACKGROUND

N-acetyl-β-D-glucosamine (GlcNAc) is widely used as a valuable pharmacological agent and a functional food additive. The traditional chemical process for GlcNAc production has some problems such as high production cost, low yield, and acidic pollution. Hence, to identify a novel chitinase that is suitable for bioconversion of chitin to GlcNAc is of great value.

RESULTS

A novel chitinase gene (PbChi74) from Paenibacillus barengoltzii was cloned and heterologously expressed in Escherichia coli as an intracellular soluble protein. The gene has an open reading frame (ORF) of 2,163 bp encoding 720 amino acids. The recombinant chitinase (PbChi74) was purified to apparent homogeneity with a purification fold of 2.2 and a recovery yield of 57.9%. The molecular mass of the purified enzyme was estimated to be 74.6 kDa and 74.3 kDa by SDS-PAGE and gel filtration, respectively. PbChi74 displayed an acidic pH optimum of 4.5 and a temperature optimum of 65°C. The enzyme showed high activity toward colloidal chitin, glycol chitin, N-acetyl chitooligosaccharides, and p-nitrophenyl N-acetyl β-glucosaminide. PbChi74 hydrolyzed colloidal chitin to yield N-acetyl chitobiose [(GlcNAc)2] at the initial stage, which was further converted to its monomer N-acetyl glucosamine (GlcNAc), suggesting that it is an exochitinase with β-N-acetylglucosaminidase activity. The purified PbChi74 coupled with RmNAG (β-N-acetylglucosaminidase from Rhizomucor miehei) was used to convert colloidal chitin to GlcNAc, and GlcNAc was the sole end product at a concentration of 27.8 mg mL(-1) with a conversion yield of 92.6%. These results suggest that PbChi74 may have great potential in chitin conversion.

CONCLUSIONS

The excellent thermostability and hydrolytic properties may give the exochitinase great potential in GlcNAc production from chitin. This is the first report on an exochitinase with N-acetyl-β-D-glucosaminidase activity from Paenibacillus species.

Characterization of cis-acting elements residing in the chitinase promoter of Bacillus pumilus SG2

Bacillus pumilus SG2 is a chitinolytic bacterium that produces two chitinases, namely ChiS and ChiL. The chiS and chiL genes are consecutively expressed under a common promoter. Regulation of the chiS and chiL genes is under the control of carbon catabolite repression (CCR) in B. pumilus. This study aimed to investigate the cis-acting elements of the chitinase promoter. For this purpose, we transferred the chiS gene along with its specific promoter to Bacillus subtilis as a host. Primer extension analysis revealed two transcription start sites located 287 and 65 bp upstream of the chiS start codon. The distal promoter was highly compatible with the consensus sequence of the σ(A)-type promoters in B. subtilis, whereas the proximal promoter sequence showed less similarity to the σ(A)-type consensus sequence. A catabolite responsive element (cre), which is required for CCR in Bacillus species, was found to be 136 to 123 bp upstream of the chiS start codon. Interestingly, this cre site was located upstream of the -35 of the proximal promoter and downstream of the distal promoter. Deletion of this cre site sequence rendered the chiS expression constitutive.

Crystallization and preliminary X-ray diffraction analysis of an active-site mutant of `loopless' family GH19 chitinase from Bryum coronatum in a complex with chitotetraose

The catalytic mechanism of family GH19 chitinases is not well understood owing to insufficient information regarding the three-dimensional structures of enzyme-substrate complexes. Here, the crystallization and preliminary X-ray diffraction analysis of a selenomethionine-labelled active-site mutant of `loopless' family GH19 chitinase from the moss Bryum coronatum in complex with chitotetraose, (GlcNAc)4, are reported. The crystals were grown using the vapour-diffusion method. They diffracted to 1.58 Å resolution using synchrotron radiation at the Photon Factory. The crystals belonged to the monoclinic space group C2, with unit-cell parameters a = 74.5, b = 58.4, c = 48.1 Å, β = 115.6°. The asymmetric unit of the crystals is expected to contain one protein molecule, with a Matthews coefficient of 2.08 Å(3) Da(-1) and a solvent content of 41%.

Cooperative degradation of chitin by extracellular and cell surface-expressed chitinases from Paenibacillus sp. strain FPU-7

Chitin, a major component of fungal cell walls and invertebrate cuticles, is an exceedingly abundant polysaccharide, ranking next to cellulose. Industrial demand for chitin and its degradation products as raw materials for fine chemical products is increasing. A bacterium with high chitin-decomposing activity, Paenibacillus sp. strain FPU-7, was isolated from soil by using a screening medium containing α-chitin powder. Although FPU-7 secreted several extracellular chitinases and thoroughly digested the powder, the extracellular fluid alone broke them down incompletely. Based on expression cloning and phylogenetic analysis, at least seven family 18 chitinase genes were found in the FPU-7 genome. Interestingly, the product of only one gene (chiW) was identified as possessing three S-layer homology (SLH) domains and two glycosyl hydrolase family 18 catalytic domains. Since SLH domains are known to function as anchors to the Gram-positive bacterial cell surface, ChiW was suggested to be a novel multimodular surface-expressed enzyme and to play an important role in the complete degradation of chitin. Indeed, the ChiW protein was localized on the cell surface. Each of the seven chitinase genes (chiA to chiF and chiW) was cloned and expressed in Escherichia coli cells for biochemical characterization of their products. In particular, ChiE and ChiW showed high activity for insoluble chitin. The high chitinolytic activity of strain FPU-7 and the chitinases may be useful for environmentally friendly processing of chitin in the manufacture of food and/or medicine.

Comparative genome analysis of Enterobacter cloacae

The Enterobacter cloacae species includes an extremely diverse group of bacteria that are associated with plants, soil and humans. Publication of the complete genome sequence of the plant growth-promoting endophytic E. cloacae subsp. cloacae ENHKU01 provided an opportunity to perform the first comparative genome analysis between strains of this dynamic species. Examination of the pan-genome of E. cloacae showed that the conserved core genome retains the general physiological and survival genes of the species, while genomic factors in plasmids and variable regions determine the virulence of the human pathogenic E. cloacae strain; additionally, the diversity of fimbriae contributes to variation in colonization and host determination of different E. cloacae strains. Comparative genome analysis further illustrated that E. cloacae strains possess multiple mechanisms for antagonistic action against other microorganisms, which involve the production of siderophores and various antimicrobial compounds, such as bacteriocins, chitinases and antibiotic resistance proteins. The presence of Type VI secretion systems is expected to provide further fitness advantages for E. cloacae in microbial competition, thus allowing it to survive in different environments. Competition assays were performed to support our observations in genomic analysis, where E. cloacae subsp. cloacae ENHKU01 demonstrated antagonistic activities against a wide range of plant pathogenic fungal and bacterial species.

Functional expression and characterization of a chitinase from the marine archaeon Halobacterium salinarum CECT 395 in Escherichia coli

The HschiA1 gene of the archaeon Halobacterium salinarum CECT 395 was cloned and overexpressed as an active protein of 66.5 kDa in Escherichia coli. The protein called HsChiA1p has a modular structure consisting of a glycosyl hydrolase family 18 catalytic region, as well as a N-terminal family 5 carbohydrate-binding module and a polycystic kidney domain. The purified recombinant chitinase displayed optimum catalytic activity at pH 7.3 and 40 °C and showed high stability over broad pH (6-8.5) and temperature (25-45 °C) ranges. Protein activity was stimulated by the metal ions Mg(+2), K(+), and Ca(+2) and strongly inhibited by Mn(+2). HsChiA1p is salt-dependent with its highest activity in the presence of 1.5 M of NaCl, but retains 20% of its activity in the absence of salt. The recombinant enzyme hydrolysed p-NP-(GlcNAc)3, p-NP-(GlcNAc), crystalline chitin, and colloidal chitin. From its sequence features and biochemical properties, it can be identified as an exo-acting enzyme with potential interest regarding the biodegradation of chitin waste or its bioconversion into biologically active products.

Chitinases: in agriculture and human healthcare

Biological control of phytopathogenic fungi and insects continues to inspire the research and development of environmentally friendly bioactive alternatives. Potentially lytic enzymes, chitinases can act as a biocontrol agent against agriculturally important fungi and insects. The cell wall in fungi and protective covers, i.e. cuticle in insects shares a key structural polymer, chitin, a β-1,4-linked N-acetylglucosamine polymer. Therefore, it is advantageous to develop a common biocontrol agent against both of these groups. As chitin is absent in plants and mammals, targeting its metabolism will signify an eco-friendly strategy for the control of agriculturally important fungi and insects but is innocuous to mammals, plants, beneficial insects and other organisms. In addition, development of chitinase transgenic plant varieties probably holds the most promising method for augmenting agricultural crop protection and productivity, when properly integrated into traditional systems. Recently, human proteins with chitinase activity and chitinase-like proteins were identified and established as biomarkers for human diseases. This review covers the recent advances of chitinases as a biocontrol agent and its various applications including preparation of medically important chitooligosaccharides, bioconversion of chitin as well as in implementing chitinases as diagnostic and prognostic markers for numerous diseases and the prospect of their future utilization.

High-yield production of a chitinase from Aeromonas veronii B565 as a potential feed supplement for warm-water aquaculture

Chitin, present in crustacean shells, insects, and fungi, is the second most plentiful natural organic fiber after wood. To effectively use chitin in a cost-saving and environmentally friendly way in aquaculture, crustacean shells (e.g., shrimp-shell meal) are supplemented into aquafeed after degradation by chemical methods. Herein, we describe a chitinase from Aeromonas veronii B565, designated ChiB565, which potently degrades shrimp-shell chitin and resists proteolysis. We isolated recombinant ChiB565 of the expected molecular mass in large yield from Pichia pastoris. ChiB565 is optimally active at pH 5.0 and 50 °C and stable between pH 4.5 and 9.0 at 50 °C and below. Compared with the commercial chitinase C-6137, which cannot degrade shrimp-shell chitin, ChiB565 hydrolyzes shrimp-shell chitin in addition to colloidal chitin, powdered chitin, and β-1,3-1,4-glucan. The optimal enzyme concentration and reaction time for in vitro degradation of 0.1 g of powdered shrimp shell are 30 U of ChiB565 and 3 h, respectively. A synergistic protein-release effect occurred when ChiB565 and trypsin were incubated in vitro with shrimp shells. Tilapia were fed an experimental diet containing 5% (w/w) shrimp bran and 16.2 U/kg ChiB565, which significantly improved growth and feed conversion compared with a control diet lacking ChiB565. Dietary ChiB565 enhanced nitrogen digestibility and downregulated intestinal IL-1β expression. The immunologically relevant protective effects of dietary ChiB565 were also observed for 2 to 3 days following exposure to pathogenic Aeromonas hydrophila.

Increase in gut microbiota after immune suppression in baculovirus-infected larvae

Spodoptera exigua microarray was used to determine genes differentially expressed in S. exigua cells challenged with the species-specific baculovirus SeMNPV as well as with a generalist baculovirus, AcMNPV. Microarray results revealed that, in contrast to the host transcriptional shut-off that is expected during baculovirus infection, S. exigua cells showed a balanced number of up- and down-regulated genes during the first 36 hours following the infection. Many immune-related genes, including pattern recognition proteins, genes involved in signalling and immune pathways as well as immune effectors and genes coding for proteins involved in the melanization cascade were found to be down-regulated after baculovirus infection. The down-regulation of immune-related genes was confirmed in the larval gut. The expression of immune-related genes in the gut is known to affect the status of gut microorganisms, many of which are responsible for growth and development functions. We therefore asked whether the down-regulation that occurs after baculovirus infection affects the amount of gut microbiota. An increase in the gut bacterial load was observed and we hypothesize this to be as a consequence of viral infection. Subsequent experiments on virus performance in the presence and absence of gut microbiota revealed that gut bacteria enhanced baculovirus virulence, pathogenicity and dispersion. We discuss the host immune response processes and pathways affected by baculoviruses, as well as the role of gut microbiota in viral infection.

Baculoviruses are large DNA viruses that infect invertebrates, mainly insects from the order Lepidoptera. They were first discovered to cause insects' epizootics and are now used worldwide as biocontrol agents. Extensive studies on baculovirus biology led to the discovery that they can serve as expression vectors in insect cells; recently they have also been considered as vectors for gene therapy. Baculovirus infection, like many other oral infections, starts with the invasion of the gut by viruses; the gut is a compartment colonized by a community of resident microbiota. In this study, we observed that baculovirus infection leads to the decreased expression of immune-related genes in a Spodoptera exigua cell culture as well as in the larval gut. Gut microbial loads were found to increase after baculovirus infection. A series of bioassays showed that the baculovirus performs better in the presence of microbiota in the gut. Our study shows that baculovirus infection leads to increase of microbiota loads in the gut and that the gut microbiota play a significant role in insect immunity and susceptibility to viral infections. These findings suggest that gut microbiota can be manipulated to improve biocontrol strategies that employ baculoviruses.

Mycolytic enzymes produced by Streptomyces violaceusniger and their role in antagonism towards wood-rotting fungi

Extracellular mycolytic enzymes produced under submerged fermentation by the fungal antagonist Streptomyces violaceusniger MTCC 3959 were characterized. This streptomycete produced higher amounts of extracellular chitinase and protease during late exponential phase, whereas β-1,3-glucanase production was at peak in mid-stationary phase. Cell-free culture filtrate (CCF) exhibited a broad range of antifungal activity against both white rot and brown rot fungi. The inhibitory activity was completely lost after treatment with proteinase K and heat, indicating that extracellular antifungal metabolites are heat labile and proteinaceous in nature. Optimum pH and temperature for enzyme activity were: 9.0 and 60 °C for chitinase; 6.0 and 60 °C for β-1,3-glucanase; and 9.0 and 70 °C for protease. Mycolytic enzymes were moderately thermostable, and had a wide pH stability range extending from pH 5.0 to 10.0. The zymogram analysis of CCF revealed five chitinase isoenzymes with an apparent molecular weight of 20.8, 33.3, 45.6, 67.4, and 114.8 kDa, one β-1,3-glucanase appeared as a single band of ∼131.8 kDa and four protease isoenzymes with approximate molecular weights of 22.8, 62.52, 74.64, and 120.5 kDa. S. violaceusniger MTCC 3959 produced mycolytic enzymes that can be effectively used for suppression of phytopathogenic basidiomycetes. It has the potential to be an effective biofungicide.

Actinomycetes: a repertory of green catalysts with a potential revenue resource

Biocatalysis, one of the oldest technologies, is becoming a favorable alternative to chemical processes and a vital part of green technology. It is an important revenue generating industry due to a global market projected at $7 billion in 2013 with a growth of 6.7% for enzymes alone. Some microbes are important sources of enzymes and are preferred over sources of plant and animal origin. As a result, more than 50% of the industrial enzymes are obtained from bacteria. The constant search for novel enzymes with robust characteristics has led to improvisations in the industrial processes, which is the key for profit growth. Actinomycetes constitute a significant component of the microbial population in most soils and can produce extracellular enzymes which can decompose various materials. Their enzymes are more attractive than enzymes from other sources because of their high stability and unusual substrate specificity. Actinomycetes found in extreme habitats produce novel enzymes with huge commercial potential. This review attempts to highlight the global importance of enzymes and extends to signify actinomycetes as promising harbingers of green technology.

The Listeria monocytogenes ChiA chitinase enhances virulence through suppression of host innate immunity

Environmental pathogens survive and replicate within the outside environment while maintaining the capacity to infect mammalian hosts. For some microorganisms, mammalian infection may be a relatively rare event. Understanding how environmental pathogens retain their ability to cause disease may provide insight into environmental reservoirs of disease and emerging infections. Listeria monocytogenes survives as a saprophyte in soil but is capable of causing serious invasive disease in susceptible individuals. The bacterium secretes virulence factors that promote cell invasion, bacterial replication, and cell-to-cell spread. Recently, an L. monocytogenes chitinase (ChiA) was shown to enhance bacterial infection in mice. Given that mammals do not synthesize chitin, the function of ChiA within infected animals was not clear. Here we have demonstrated that ChiA enhances L. monocytogenes survival in vivo through the suppression of host innate immunity. L. monocytogenes ΔchiA mutants were fully capable of establishing bacterial replication within target organs during the first 48 h of infection. By 72 to 96 h postinfection, however, numbers of ΔchiA bacteria diminished, indicative of an effective immune response to contain infection. The ΔchiA-associated virulence defect could be complemented in trans by wild-type L. monocytogenes, suggesting that secreted ChiA altered a target that resulted in a more permissive host environment for bacterial replication. ChiA secretion resulted in a dramatic decrease in inducible nitric oxide synthase (iNOS) expression, and ΔchiA mutant virulence was restored in NOS2^−/− mice lacking iNOS. This work is the first to demonstrate modulation of a specific host innate immune response by a bacterial chitinase.

Bacterial chitinases have traditionally been viewed as enzymes that either hydrolyze chitin as a food source or serve as a defense mechanism against organisms containing structural chitin (such as fungi). Recent evidence indicates that bacterial chitinases and chitin-binding proteins contribute to pathogenesis, primarily via bacterial adherence to chitin-like molecules present on the surface of mammalian cells. In contrast, mammalian chitinases have been linked to immunity via inflammatory immune responses that occur outside the context of infection, and since mammals do not produce chitin, the targets of these mammalian chitinases have remained elusive. This work demonstrates that a Listeria monocytogenes-secreted chitinase has distinct functional roles that include chitin hydrolysis and suppression of host innate immunity. The established link between chitinase and the inhibition of host inducible nitric oxide synthase (iNOS) expression may help clarify the thus far elusive relationship observed between mammalian chitinase enzymes and host inflammatory responses occurring in the absence of infection.

Overexpression, crystallization and preliminary X-ray crystallographic analysis of β-N-acetylglucosaminidase from Thermotoga maritima encoded by the Tm0809 gene

β-N-acetylglucosaminidase (NagA) protein hs a chitin-degrading activity and chitin is one of the most abundant polymers in nature. NagA contains a family 3 glycoside (GH3)-type N-terminal domain and a unique C-terminal domain. The structurally uncharacterized C-terminal domain of NagA may be involved in substrate specificity. To provide a structural basis for the substrate specificity of NagA, structural analysis of NagA from Thermotoga maritima encoded by the Tm0809 gene was initiated. NagA from T. maritima has been overexpressed in Escherichia coli and crystallized at 296 K using ammonium sulfate as a precipitant. Crystals of T. maritima NagA diffracted to 3.80 Å resolution and belonged to the monoclinic space group C2, with unit-cell parameters a = 231.15, b = 133.62, c = 140.88 Å, β = 89.97°. The crystallization of selenomethionyl-substituted protein is in progress to solve the crystal structure of T. maritima NagA.

Chitinases: An update

Chitin, the second most abundant polysaccharide in nature after cellulose, is found in the exoskeleton of insects, fungi, yeast, and algae, and in the internal structures of other vertebrates. Chitinases are enzymes that degrade chitin. Chitinases contribute to the generation of carbon and nitrogen in the ecosystem. Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications, especially the chitinases exploited in agriculture fields to control pathogens. Chitinases have a use in human health care, especially in human diseases like asthma. Chitinases have wide-ranging applications including the preparation of pharmaceutically important chitooligosaccharides and N-acetyl D glucosamine, preparation of single-cell protein, isolation of protoplasts from fungi and yeast, control of pathogenic fungi, treatment of chitinous waste, mosquito control and morphogenesis, etc. In this review, the various types of chitinases and the chitinases found in different organisms such as bacteria, plants, fungi, and mammals are discussed.

Microbial mechanisms mediating increased soil C storage under elevated atmospheric N deposition

Future rates of anthropogenic N deposition can slow the cycling and enhance the storage of C in forest ecosystems. In a northern hardwood forest ecosystem, experimental N deposition has decreased the extent of forest floor decay, leading to increased soil C storage. To better understand the microbial mechanisms mediating this response, we examined the functional genes derived from communities of actinobacteria and fungi present in the forest floor using GeoChip 4.0, a high-throughput functional-gene microarray. The compositions of functional genes derived from actinobacterial and fungal communities was significantly altered by experimental nitrogen deposition, with more heterogeneity detected in both groups. Experimental N deposition significantly decreased the richness and diversity of genes involved in the depolymerization of starch (∼12%), hemicellulose (∼16%), cellulose (∼16%), chitin (∼15%), and lignin (∼16%). The decrease in richness occurred across all taxonomic groupings detected by the microarray. The compositions of genes encoding oxidoreductases, which plausibly mediate lignin decay, were responsible for much of the observed dissimilarity between actinobacterial communities under ambient and experimental N deposition. This shift in composition and decrease in richness and diversity of genes encoding enzymes that mediate the decay process has occurred in parallel with a reduction in the extent of decay and accumulation of soil organic matter. Our observations indicate that compositional changes in actinobacterial and fungal communities elicited by experimental N deposition have functional implications for the cycling and storage of carbon in forest ecosystems.

Backbone chemical shifts assignments, secondary structure, and ligand binding of a family GH-19 chitinase from moss, Bryum coronatum

Family GH19 chitinases have been recognized as important in the plant defense against fungal pathogens. However, their substrate-recognition mechanism is still unknown. We report here the first resonance assignment of NMR spectrum of a GH19 chitinase from moss, Bryum coronatum (BcChi-A). The backbone signals were nearly completely assigned, and the secondary structure was estimated based on the chemical shift values. The addition of the chitin dimer to the enzyme solution perturbed the chemical shifts of HSQC resonances of the amino acid residues forming the putative substrate-binding cleft. Further NMR analysis of the ligand binding to BcChi-A will improve understanding of the substrate-recognition mechanism of GH-19 enzymes.

Purification and characterization of an extracellular chitinase from antagonistic Streptomyces violaceusniger

The actinomycetes Streptomyces violaceusniger showed strong antagonistic activity against various tested wood rotting fungi. An extracellular chitinase, produced by antagonistic S. violaceusniger MTCC 3959, was purified as follows: ammonium sulfate precipitation, chitin affinity and chromatographic separation of Q Sepharose. The molecular mass of the purified chitinase was estimated as 56.5 kDa by SDS-PAGE. Chitinase was optimally active at pH of 5.0 and 50 °C. It retained almost 100% activity at pH 5.0 and also had high thermal tolerance at 50 °C. Enzyme activity was inhibited by Hg(2+) and Ag(+) cations, but was neither substantially inhibited by K(+) cation nor by chelating agent EDTA. The apparent Km and Vmax at 37 °C were 0.1426 mM and 6.6 U/mg, respectively using pNP-(GlcNAc)2 as substrate. The 56.5 kDa chitinase of strain MTCC 3959 represented an exo-type activity. The purified chitinase was further identified by MALDI-TOF. The results of peptide mass fingerprinting showed that 10 tryptic peptides of the chitinase were identical to the chitinase C from Streptomyces albus J1074 (GenBank Accession No. gi|239982330). The sequence of N-terminal amino acid (AA) of the chitinase was determined to be G-D-G-T-G-P-G-P-G-P.

Synthesis of long-chain chitooligosaccharides by a hypertransglycosylating processive endochitinase of Serratia proteamaculans 568

We describe the heterologous expression and characterization of a 407-residue single-domain glycosyl hydrolase family 18 chitinase (SpChiD) from Gram-negative Serratia proteamaculans 568 that has unprecedented catalytic properties. SpChiD was optimally active at pH 6.0 and 40 °C, where it showed a K(m) of 83 mg ml(-1), a k(cat) of 3.9 × 10(2) h(-1), and a k(cat)/K(m) of 4.7 h mg(-1) ml(-1) on colloidal chitin. On chitobiose, the K(m), k(cat), and k(cat)/K(m) were 203 μM, 1.3 × 10(2) h(-1), and 0.62 h(-1) μM(-1), respectively. Hydrolytic activity on chitooligosaccharides (CHOS) and colloidal chitin indicated that SpChiD was an endo-acting processive enzyme, with the unique ability to convert released chitobiose to N-acetylglucosamine, the major end product. SpChiD showed hyper transglycosylation (TG) with trimer-hexamer CHOS substrates, generating considerable amounts of long-chain CHOS. The TG activity of SpChiD was dependent on both the length and concentration of the oligomeric substrate and also on the enzyme concentration. The length and amount of accumulated TG products increased with increases in the length of the substrate and its concentration and decreased with increases in the enzyme concentration. The SpChiD bound to insoluble and soluble chitin substrates despite the absence of accessory domains. Sequence alignments and structural modeling indicated that SpChiD would have a deep substrate-binding groove lined with aromatic residues, which is characteristic of processive enzymes. SpChiD shows a combination of properties that seems rare among family 18 chitinases and that may resemble the properties of human chitotriosidase.

Purification and characterization of a 56 kDa chitinase isozyme (PaChiB) from the stomach of the silver croaker, Pennahia argentatus

A 56 kDa chitinase isozyme (PaChiB) was purified from the stomach of the silver croaker Pennahia argentatus. The optimum pH and pH stability of PaChiB were observed in an acidic pH range. When N-acetylchitooligosaccharides ((GlcNAc)n, n=2 -6) were used as substrates, PaChiB degraded (GlcNAc)4 -6 and produced (GlcNAc)2,3. It degraded (GlcNAc)5 to produce (GlcNAc)2 (23.2%) and (GlcNAc)3 (76.8%). The ability to degrade p-nitrophenyl N-acetylchitooligosaccharides (pNp-(GlcNAc)n, n=2 -4) fell in the following order: pNp-(GlcNAc)3≫ pNp-(GlcNAc)2 pNp-(GlcNAc)4. Based on these results, we concluded that PaChiB is an endo-type chitinolytic enzyme, and that it preferentially hydrolyzes the third glycosidic bond from the non-reducing end of (GlcNAc)n. Activity toward crystalline α- and β-chitin was activated at 124%-185% in the presence of 0.5 M NaCl. PaChiB exhibited markedly high substrate specificity toward crab-shell α-chitin.

Purification, characterization of a CkChn134 protein from Cynanchum komarovii seeds and synergistic effect with CkTLP against Verticillium dahliae

Cynanchum komarovii Al Iljinski is a desert plant that has been used as analgesic, anthelminthic, and antidiarrheal, but also as herbal medicine to treat cholecystitis in people. In this work, an antifungal protein with sequence homology to chitinase was isolated from C. komarovii seeds and named CkChn134. The three-dimensional structure prediction of CkChn134 indicated that the protein has a loop domain formed a thin cleft, which is able to bind molecules and substrates. The protein and CkTLP synergistically inhibited the fungal growth of Verticillium dahliae, Fusarium oxysporum, Rhizoctonia solani, Botrytis cinerea, and Valsa mali in vitro. The full-length cDNA was cloned by RT-PCR and RACE-PCR according to the partial protein sequences obtained by nanoESI-MS/MS. The real-time PCR showed that the transcription level of CkChn134 had a significant increase under the stress of ethylene, NaCl, low temperature, drought, and pathogen infection, which indicates that CkChn134 may play an important role in response to abiotic and biotic stresses. The CkChn134 protein was located in the extracellular space/cell wall by CkChn134::GFP fusion protein in transgenic Arabidopsis. Furthermore, overexpression of CkChn134 significantly enhanced the resistance of transgenic Arabidopsis against V. dahliae. Interestingly, the coexpression of CkChn134 and CkTLP showed substantially greater protection against the fungal pathogen V. dahliae than either transgene alone. The results suggest that the CkChn134 is a good candidate protein or gene, and it had a potential synergistic effect with CkTLP for contributing to the development of disease-resistant crops.

Chitinase production by Bacillus thuringiensis and Bacillus licheniformis: their potential in antifungal biocontrol

Thirty bacterial strains were isolated from the rhizosphere of plants collected from Egypt and screened for production of chitinase enzymes. Bacillus thuringiensis NM101-19 and Bacillus licheniformis NM120-17 had the highest chitinolytic activities amongst those investigated. The production of chitinase by B. thuringiensis and B. licheniformis was optimized using colloidal chitin medium amended with 1.5% colloidal chitin, with casein as a nitrogen source, at 30°C after five days of incubation. An enhancement of chitinase production by the two species was observed by addition of sugar substances and dried fungal mats to the colloidal chitin media. The optimal conditions for chitinase activity by B. thuringiensis and B. licheniformis were at 40°C, pH 7.0 and pH 8.0, respectively. Na(+), Mg(2+), Cu(2+), and Ca(2+) caused enhancement of enzyme activities whereas they were markedly inhibited by Zn(2+), Hg(2+), and Ag(+). In vitro, B. thuringiensis and B. licheniformis chitinases had potential for cell wall lysis of many phytopathogenic fungi tested. The addition of B. thuringiensis chitinase was more effective than that of B. licheniformis in increasing the germination of soybean seeds infected with various phytopathogenic fungi.