High-multiplicity of chitinase genes in Streptomyces coelicolor A3(2)

Characterization of the extracellular domain of sensor histidine kinase NagS from Paenibacillus sp. str. FPU-7: nagS interacts with oligosaccharide binding protein NagB1 in complexes with N, N'-diacetylchitobiose

We have previously isolated the Gram-positive chitin-degrading bacterium Paenibacillus sp. str. FPU-7. This bacterium traps chitin disaccharide (GlcNAc)2 on its cell surface using two homologous solute-binding proteins, NagB1 and NagB2. Bacteria use histidine kinase (HK) of the two-component regulatory system as an extracellular environment sensor. In this study, we found that nagS, which encodes a HK, is located next to the nagB1 gene. Biochemical experiments revealed that the NagS sensor domain (NagS30-294) interacts with the NagB1-(GlcNAc)2 complex. However, proof of NagS30-294 interacting with NagB1 without (GlcNAc)2 is currently unavailable. In contrast to NagB1, no complex formation was observed between NagS30-294 and NagB2, even in the presence of (GlcNAc)2. The NagS30-294 crystal structure at 1.8 Å resolution suggested that the canonical tandem-Per-Arnt-Sim fold recognizes the NagB1-(GlcNAc)2 complex. This study provides insight into the recognition of chitin oligosaccharides by bacteria.

Chitin Biodegradation by Lytic Polysaccharide Monooxygenases from Streptomyces coelicolor In Vitro and In Vivo

Lytic polysaccharide monooxygenases (LPMOs) have the potential to improve recalcitrant polysaccharide hydrolysis by the oxidizing cleavage of glycosidic bond. Streptomyces species are major chitin decomposers in soil ecological environments and encode multiple lpmo genes. In this study, we demonstrated that transcription of the lpmo gene, Sclpmo10G, in the Streptomyces coelicolor A3(2) (ScA3(2)) strain is strongly induced by chitin. The ScLPMO10G protein was further expressed in Escherichia coli and characterized in vitro. The ScLPMO10G protein showed oxidation activity towards chitin. Chitinase synergy experiments demonstrated that the addition of ScLPMO10G resulted in a substantial in vitro increase in the reducing sugar levels. Moreover, in vivo the LPMO-overexpressing strain ScΔLPMO10G(+) showed stronger chitin-degrading ability than the wild-type, leading to a 2.97-fold increase in reducing sugar level following chitin degradation. The total chitinase activity of ScΔLPMO10G(+) was 1.5-fold higher than that of ScA3(2). In summary, ScLPMO10G may play a role in chitin biodegradation in S. coelicolor, which could have potential applications in biorefineries.

Structures and functions of carbohydrate-active enzymes of chitinolytic bacteria Paenibacillus sp. str. FPU-7

Chitin and its derivatives have valuable potential applications in various fields that include medicine, agriculture, and food industries. Paenibacillus sp. str. FPU-7 is one of the most potent chitin-degrading bacteria identified. This review introduces the chitin degradation system of P. str. FPU-7. In addition to extracellular chitinases, P. str. FPU-7 uses a unique multimodular chitinase (ChiW) to hydrolyze chitin to oligosaccharides on the cell surface. Chitin oligosaccharides are converted to N-acetyl-d-glucosamine by β-N-acetylhexosaminidase (PsNagA) in the cytosol. The functions and structures of ChiW and PsNagA are also summarized. The genome sequence of P. str. FPU-7 provides opportunities to acquire novel enzymes. Genome mining has identified a novel alginate lyase, PsAly. The functions and structure of PsAly are reviewed. These findings will inform further improvement of the sustainable conversion of polysaccharides to functional materials.

Structural characterization of two solute-binding proteins for N,N'-diacetylchitobiose/N,N',N''-triacetylchitotoriose of the gram-positive bacterium, Paenibacillus sp. str. FPU-7

The chitinolytic bacterium Paenibacillus sp. str. FPU-7 efficiently degrades chitin into oligosaccharides such as N-acetyl-D-glucosamine (GlcNAc) and disaccharides (GlcNAc)₂ through multiple secretory chitinases. Transport of these oligosaccharides by P. str. FPU-7 has not yet been clarified. In this study, we identified nagB1, predicted to encode a sugar solute-binding protein (SBP), which is a component of the ABC transport system. However, the genes next to nagB1 were predicted to encode two-component regulatory system proteins rather than transmembrane domains (TMDs). We also identified nagB2, which is highly homologous to nagB1. Adjacent to nagB2, two genes were predicted to encode TMDs. Binding experiments of the recombinant NagB1 and NagB2 to several oligosaccharides using differential scanning fluorimetry and surface plasmon resonance confirmed that both proteins are SBPs of (GlcNAc)₂ and (GlcNAc)₃. We determined their crystal structures complexed with and without chitin oligosaccharides at a resolution of 1.2 to 2.0 Å. The structures shared typical SBP structural folds and were classified as subcluster D-I. Large domain motions were observed in the structures, suggesting that they were induced by ligand binding via the "Venus flytrap" mechanism. These structures also revealed chitin oligosaccharide recognition mechanisms. In conclusion, our study provides insight into the recognition and transport of chitin oligosaccharides in bacteria.

Biocontrol potential of chitinases produced by newly isolated Chitinophaga sp. S167

A chitinolytic bacterium Chitinophaga sp. S167 producing extracellular chitinases was isolated from a soil sample in India. The extracellular chitinases produced by S167 were concentrated by ammonium sulphate precipitation (AS70) and seven bands corresponding to chitinases were observed by zymography. Optimum temperature and pH of AS70 were between 40 and 45 °C and pH 6.0 respectively with high stability at 20-40 °C and pH 5-7. AS70 inhibited the growth of Fusarium oxysporum, Alternaria alternata and Cladosporium sp. in vitro. The culture conditions for the high level production of extracellular chitinases were optimized resulting in 48-folds higher chitinase production. As the combination of chitinases could be more potent in biocontrol of plant diseases, it was checked if AS70 could control postharvest fungal infection caused by Fusarium oxysporum on tomatoes. AS70 treated tomatoes showed significant lower incidence of infection (11%) by F. oxysporum as compared with 100% in the control at 5 days post inoculation. Further, AS70 caused significant mortality in second stage juveniles of root knot nematode, Meloidogyne incognita, a major agriculture pest responsible for economic losses in agriculture. This study highlights the antifungal and nematicidal activity of chitinases produced by Chitinophaga sp. S167. To the best of our knowledge, this is the first report of the biocontrol potential of the chitinases produced by Chitinophaga sp.

Two Highly Similar Chitinases from Marine Vibrio Species have Different Enzymatic Properties

Chitinase, as one of the most important extracellular enzymes in the marine environment, has great ecological and applied values. In this study, two chitinases (Chi1557 and Chi4668) with 97.33% amino acid sequences identity were individually found in Vibrio rotiferianus and Vibrio harveyi. They both were encoding by 561 amino acids, but differed in 15 amino acids and showed different enzymatic properties. The optimal temperature and pH ranges were 45-50 °C and pH 5.0-7.0 for Chi1557, while ~50 °C and pH 3.0-6.0 for Chi4668. K+, Mg2+, and EDTA increased the enzymatic activity of Chi4668 significantly, yet these factors were inhibitory to Chi1557. Moreover, Chi1557 degraded colloidal chitin to produce (GlcNAc)2 and minor GlcNAc, whereas Chi4668 produce (GlcNAc)2 with minor (GlcNAc)3 and (GlcNAc)4. The Kcat/Km of Chi4668 was ~4.7 times higher than that of Chi1557, indicating that Chi4668 had stronger catalytic activity than Chi1557. Furthermore, site-directed mutagenesis was performed on Chi1557 focusing on seven conserved amino acid residues of family GH18 chitinases. Chi1557 was almost completely inactive after Glu154, Gln219, Tyr221, or Trp312 was individually mutated, retained ~50% activity after Tyr37 was mutated, and increased two times activity after Asp152 was mutated, indicating that these six amino acids were key sites for Chi1557.

Structural and functional characterization of a glycoside hydrolase family 3 β-N-acetylglucosaminidase from Paenibacillus sp. str. FPU-7

Chitin, a β-1,4-linked homopolysaccharide of N-acetyl-d-glucosamine (GlcNAc), is one of the most abundant biopolymers on Earth. Paenibacillus sp. str. FPU-7 produces several different chitinases and converts chitin into N,N′-diacetylchitobiose ((GlcNAc)2) in the culture medium. However, the mechanism by which the Paenibacillus species imports (GlcNAc)2 into the cytoplasm and divides it into the monomer GlcNAc remains unclear. The gene encoding Paenibacillus β-N-acetyl-d-glucosaminidase (PsNagA) was identified in the Paenibacillus sp. str. FPU-7 genome using an expression cloning system. The deduced amino acid sequence of PsNagA suggests that the enzyme is a part of the glycoside hydrolase family 3 (GH3). Recombinant PsNagA was successfully overexpressed in Escherichia coli and purified to homogeneity. As assessed by gel permeation chromatography, the enzyme exists as a 57-kDa monomer. PsNagA specifically hydrolyses chitin oligosaccharides, (GlcNAc)2–4, 4-nitrophenyl N-acetyl β-d-glucosamine (pNP-GlcNAc) and pNP-(GlcNAc)2–6, but has no detectable activity against 4-nitrophenyl β-d-glucose, 4-nitrophenyl β-d-galactosamine and colloidal chitin. In this study, we present a 1.9 Å crystal structure of PsNagA bound to GlcNAc. The crystal structure reveals structural features related to substrate recognition and the catalytic mechanism of PsNagA. This is the first study on the structural and functional characterization of a GH3 β-N-acetyl-d-glucosaminidase from Paenibacillus sp.

Bacterial Chitinase System as a Model of Chitin Biodegradation

Chitin, a structural polysaccharide of β-1,4-linked N-acetyl-D-glucosamine residues, is the second most abundant natural biopolymer after cellulose. The metabolism of chitin affects the global carbon and nitrogen cycles, which are maintained by marine and soil-dwelling bacteria. The degradation products of chitin metabolism serve as important nutrient sources for the chitinolytic bacteria. Chitinolytic bacteria have elaborate enzymatic systems for the degradation of the recalcitrant chitin biopolymer. This chapter introduces chitin degradation and utilization systems of the chitinolytic bacteria. These bacteria secrete many chitin-degrading enzymes, including processive chitinases, endo-acting non-processive chitinases, lytic polysaccharide monooxygenases, and N-acetyl-hexosaminidases. Bacterial chitinases play a fundamental role in the degradation of chitin. Enzymatic properties, catalytic mechanisms, and three-dimensional structures of chitinases have been extensively studied by many scientists. These enzymes can be exploited to produce a range of chitin-derived products, e.g., biocontrol agents against many plant pathogenic fungi and insects. We introduce bacterial chitinases in terms of their reaction modes and structural features.

Chitinolytic functions in actinobacteria: ecology, enzymes, and evolution

Actinobacteria, a large group of Gram-positive bacteria, secrete a wide range of extracellular enzymes involved in the degradation of organic compounds and biopolymers including the ubiquitous aminopolysaccharides chitin and chitosan. While chitinolytic enzymes are distributed in all kingdoms of life, actinobacteria are recognized as particularly good decomposers of chitinous material and several members of this taxon carry impressive sets of genes dedicated to chitin and chitosan degradation. Degradation of these polymers in actinobacteria is dependent on endo- and exo-acting hydrolases as well as lytic polysaccharide monooxygenases. Actinobacterial chitinases and chitosanases belong to nine major families of glycosyl hydrolases that share no sequence similarity. In this paper, the distribution of chitinolytic actinobacteria within different ecosystems is examined and their chitinolytic machinery is described and compared to those of other chitinolytic organisms.

A new chitinase-D from a plant growth promoting Serratia marcescens GPS5 for enzymatic conversion of chitin

The current study describes heterologous expression and biochemical characterization of single-modular chitinase-D from Serratia marcescens (SmChiD) with unprecedented catalytic properties which include chitobiase and transglycosylation (TG) activities besides hydrolytic activity. Without accessory domains, SmChiD, hydrolyzed insoluble polymeric chitin substrates like colloidal, α- and β-chitin. Activity studies on CHOS with degree of polymerization (DP) 2-6 as substrate revealed that SmChiD hydrolyzed DP2 with a chitobiase activity and showed TG activity on CHOS with DP3-6, producing longer chain CHOS. But, the TG products were further hydrolyzed to shorter chain CHOS with DP1-2 products. SmChiD with its unique catalytic properties, could be a potential enzyme for the production of long chain CHOS and also for the preparation of efficient enzyme cocktails for chitin degradation.

Three dimensional (3D) structure prediction and substrate-protein interaction study of the chitin binding protein CBP24 from B. thuringiensis

Bacillus thuringiensis is an insecticidal bacterium whose chitinolytic system has been exploited to improve insect resistance in crops. In the present study, we studied the CBP24 from B. thuringiensis using homology modeling and molecular docking. The primary and secondary structure analyses showed CBP24 is a positively charged protein and contains single domain that belongs to family CBM33. The 3D model after refinement was used to explore the chitin binding characteristics of CBP24 using AUTODOCK. The docking analyses have shown that the surface exposed hydrophilic amino acid residues Thr-103, Lys-112 and Ser-162 interact with substrate through H-bonding. While, the amino acids resides Glu-39, Tyr-46, Ser-104 and Asn-109 were shown to have polar interactions with the substrate. The binding energy values evaluation of docking depicts a stable intermolecular conformation of the docked complex. The functional characterization of the CBP24 will elucidate the substrate-interaction pathway of the protein in specific and the carbohydrate binding proteins in general leading towards the exploration and exploitation of the prokaryotic substrate utilization pathways.

Bacterial chitin degradation-mechanisms and ecophysiological strategies

Chitin is one the most abundant polymers in nature and interacts with both carbon and nitrogen cycles. Processes controlling chitin degradation are summarized in reviews published some 20 years ago, but the recent use of culture-independent molecular methods has led to a revised understanding of the ecology and biochemistry of this process and the organisms involved. This review summarizes different mechanisms and the principal steps involved in chitin degradation at a molecular level while also discussing the coupling of community composition to measured chitin hydrolysis activities and substrate uptake. Ecological consequences are then highlighted and discussed with a focus on the cross feeding associated with the different habitats that arise because of the need for extracellular hydrolysis of the chitin polymer prior to metabolic use. Principal environmental drivers of chitin degradation are identified which are likely to influence both community composition of chitin degrading bacteria and measured chitin hydrolysis activities.

Degradation of Poly(ε-caprolactone) by thermophilic Streptomyces thermoviolaceus subsp. thermoviolaceus 76T-2

A thermophilic Streptomyces thermoviolaceus subsp. thermoviolaceus isolate 76T-2 that can degrade poly(ε-caprolactone) (PCL) was isolated from soil in Taiwan. Isolate 76T-2 grew well in urea fructose oatmeal medium and exhibited clear zones on agar plates containing PCL, indicating the presence of extracellular PCL depolymerases. The PCL powder present in culture medium was completely degraded within 6 h of culture at 45°C. Two PCL-degrading enzymes were purified to homogeneity from the culture supernatant. The molecular weights of these two enzymes were estimated to be 25 kDa and 55 kDa, respectively. A portion of the N-terminal region of the 25-kDa protein was determined, and the sequence Ala-Asn-Phe-Val-Val-Ser-Glu-Ala thus obtained was identical to that of A₆₄-A₇₁ of the Chi25 chitinase of Streptomyces thermoviolaceus OPC-520. The 25-kDa protein was shown to also degrade chitin, suggesting that isolate 76T-2 has the ability to degrade both PCL and chitin.

Chitin oligosaccharide binding to a family GH19 chitinase from the moss Bryum coronatum

Substrate binding of a family GH19 chitinase from a moss species, Bryum coronatum (BcChi-A, 22 kDa), which is smaller than the 26 kDa family GH19 barley chitinase due to the lack of several loop regions ('loopless'), was investigated by oligosaccharide digestion, thermal unfolding experiments and isothermal titration calorimetry (ITC). Chitin oligosaccharides [β-1,4-linked oligosaccharides of N-acetylglucosamine with a polymerization degree of n, (GlcNAc)(n), n = 3-6] were hydrolyzed by BcChi-A at rates in the order (GlcNAc)(6) > (GlcNAc)(5) > (GlcNAc)(4) >> (GlcNAc)(3). From thermal unfolding experiments using the inactive BcChi-A mutant (BcChi-A-E61A), in which the catalytic residue Glu61 is mutated to Ala, we found that the transition temperature (T(m) ) was elevated upon addition of (GlcNAc)(n) (n = 2-6) and that the elevation (ΔT(m)) was almost proportional to the degree of polymerization of (GlcNAc)(n). ITC experiments provided the thermodynamic parameters for binding of (GlcNAc)(n) (n = 3-6) to BcChi-A-E61A, and revealed that the binding was driven by favorable enthalpy changes with unfavorable entropy changes. The change in heat capacity (ΔC(p)°) for (GlcNAc)(6) binding was found to be relatively small (-105 ± 8 cal·K(-1) ·mol(-1)). The binding free energy changes for (GlcNAc)(6), (GlcNAc)(5), (GlcNAc)(4) and (GlcNAc)(3) were determined to be -8.5, -7.9, -6.6 and -5.0 kcal·mol(-1), respectively. Taken together, the substrate binding cleft of BcChi-A consists of at least six subsites, in contrast to the four-subsites binding cleft of the 'loopless' family 19 chitinase from Streptomyces coelicolor.

DATABASE

Chitinase, EC 3.2.1.14.

High expression levels of chitinase genes in Streptomyces coelicolor A3(2) grown in soil

Although Streptomyces species are major chitin-degraders in soil ecosystems, the expression of the diverse chitinase genes within Streptomyces coelicolor grown in soil has not been assessed. As a first step, the induction pattern of nine chitinase genes in S. coelicolor growing in autoclaved soil was compared with those in liquid cultures. The relative expression levels of nine chitinase genes were measured using real-time reverse transcription PCR. The expression of all chitinase genes was induced by chitin in both autoclaved soil and liquid cultures, but to different levels. The expression levels of five chitinase genes in autoclaved soil were significantly higher than those in the liquid cultures. In particular, a putative chitinase gene, chitinase H, showed the highest induction in autoclaved soil. The same induction pattern was confirmed in nonautoclaved soil, indicating that soil contains some factors affecting the expression of chitinase genes. The chiH gene product, ChiH, cloned in Streptomycetes lividans was secreted and exhibited chitin degradation activity that was stable within a wide range of acidic pHs. The disruption of dasR, a transcriptional regulator for the uptake of N-acetylglucosamine, abolished the expression of chiH, demonstrating that DasR is required for the regulation of ChiH expression.

Molecular characterization of the modular chitin binding protein Cbp50 from Bacillus thuringiensis serovar konkukian

Bacillus thuringiensis is an insecticidal bacterium whose chitinolytic system may be exploited to improve the insecticidal system of Bt-crops. A nucleotide fragment of 1368 bp from B. thuringiensis serovar konkukian S4, containing the complete coding sequence of the chitin binding protein Cbp50, was cloned and sequenced. Analyses have shown the protein to contain a modular structure consisting of an N-terminal CBM33 domain, two copies of a fibronectin-like domain and a C-terminal chitin binding domain classified as CBM5. The Cbp50 protein was heterologously expressed in Escherichia coli, purified and assessed for chitin binding activity. A deletion mutant (CBD-N; containing only the N-terminal CBM33 domain) of Cbp50 was produced to determine the role of C-terminal domains in the binding activity of the protein. The full-length Cbp50 was shown to bind β-chitin most efficiently followed by α-chitin, colloidal chitin and cellulose. The polysaccharide binding activity of CBD-N was drastically decreased. The data demonstrate that both the N-terminal and C-terminal domains of Cbp50 are essential for the efficient binding of chitin. The purified Cbp50 showed antifungal activity against the phytopathogenic fungus Fusarium oxysporum and the opportunistic human pathogen Aspergillus niger. This is the first report of a modular chitin binding protein in bacteria.

Chitosanase from Streptomyces coelicolor A3(2): biochemical properties and role in protection against antibacterial effect of chitosan

Chitosan, an N-deacetylated derivative of chitin, has attracted much attention as an antimicrobial agent against fungi, bacteria, and viruses. Chitosanases, the glycoside hydrolases responsible for chitosan depolymerisation, are intensively studied as tools for biotechnological transformation of chitosan. The chitosanase CsnA (SCO0677) from Streptomyces coelicolor A3(2) was purified and characterized. CsnA belongs to the GH46 family of glycoside hydrolases. However, it is secreted efficiently by the Tat translocation pathway despite its similarity to the well-studied chitosanase from Streptomyces sp. N174 (CsnN174), which is preferentially secreted through the Sec pathway. Melting point determination, however, revealed substantial differences between these chitosanases, both in the absence and in the presence of chitosan. We further assessed the role of CsnA as a potential protective enzyme against the antimicrobial effect of chitosan. A Streptomyces lividans TK24 strain in which the csnA gene was inactivated by gene disruption was more sensitive to chitosan than the wild-type strain or a chitosanase-overproducing strain. This is the first genetic evidence for the involvement of chitosanases in the protection of bacteria against the antimicrobial effect of chitosan.

Degradation of chitosans with chitinase G from Streptomyces coelicolor A3(2): production of chito-oligosaccharides and insight into subsite specificities

We have studied the degradation of soluble heteropolymeric chitosans with a bacterial family 19 chitinase, ChiG from Streptomyces coelicolor A3(2), to obtain insight into the mode of action of ChiG, to determine subsite preferences for acetylated and deacetylated sugar units, and to evaluate the potential of ChiG for production of chito-oligosaccharides. Degradation of chitosans with varying degrees of acetylation was followed using NMR for the identity (acetylated/deacetylated) of new reducing and nonreducing ends as well as their nearest neighbors and using gel filtration to analyze the size distribution of the oligomeric products. Degradation of a 64% acetylated chitosan yielded a continuum of oligomers, showing that ChiG operates according to a nonprocessive, endo mode of action. The kinetics of the degradation showed an initial rapid phase dominated by cleavage of three consecutive acetylated units (A; occupying subsites -2, -1, and +1), and a slower kinetic phase reflecting the cleavage of the glycosidic linkage between a deacetylated unit (D, occupying subsite -1) and an A (occupying subsite +1). Characterization of isolated oligomer fractions obtained at the end of the initial rapid phase and at the end of the slower kinetic phase confirmed the preference for A binding in subsites -2, -1, and +1 and showed that oligomers with a deacetylated reducing end appeared only during the second kinetic phase. After maximum conversion of the chitosan, the dimers AD/AA and the trimer AAD were the dominating products. Degradation of chitosans with varying degrees of acetylation to maximum degree of scission produced a wide variety of oligomer mixtures, differing in chain length and composition of acetylated/deacetylated units. These results provide insight into the properties of bacterial family 19 chitinases and show how these enzymes may be used to convert chitosans to several types of chito-oligosaccharide mixtures.

Characterization of antifungal chitinase from marine Streptomyces sp. DA11 associated with South China Sea sponge Craniella australiensis

The gene cloning, purification, properties, kinetics, and antifungal activity of chitinase from marine Streptomyces sp. DA11 associated with South China sponge Craniella australiensis were investigated. Alignment analysis of the amino acid sequence deduced from the cloned conserved 451 bp DNA sequence shows the chitinase belongs to ChiC type with 80% similarity to chitinase C precursor from Streptomyces peucetius. Through purification by 80% ammonium sulfate, affinity binding to chitin and diethylaminoethyl-cellulose anion-exchange chromatography, 6.15-fold total purification with a specific activity of 2.95 Umg(-1) was achieved. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed a molecular weight of approximately 34 kDa and antifungal activities were observed against Aspergillus niger and Candida albicans. The optimal pH, temperature, and salinity for chitinase activity were 8.0, 50 degrees C, and 45 g per thousand psu, respectively, which may contribute to special application of this marine microbe-derived chitinase compared with terrestrial chitinases. The chitinase activity was increased by Mn(2+), Cu(2+), and Mg(2+), while strongly inhibited by Fe(2+) and Ba(2+). Meanwhile, SDS, ethyleneglycoltetraacetic acid, urea, and ethylenediaminetetraacetic acid were found to have significantly inhibitory effect on chitinase activity. With colloidal chitin as substrates instead of powder chitin, higher V (max) (0.82 mg product/min.mg protein) and lower K (m) (0.019 mg/ml) values were achieved. The sponge's microbial symbiont with chitinase activity may contribute to chitin degradation and antifungal defense. To our knowledge, it was the first time to study sponge-associated microbial chitinase.

New role of C-terminal 30 amino acids on the insoluble chitin hydrolysis in actively engineered chitinase from Vibrio parahaemolyticus

A chitinase (VpChiA) and its C-terminal truncated G589 mutant (VpChiAG589) of Vibrio parahaemolyticus were cloned by polymerase chain reaction (PCR) techniques. To study the role of the C-terminal 30 amino acids of VpChiA in the enzymatic hydrolysis of chitin, both the recombinant VpChiA and VpChiAG589 encoded in 1,881 and 1,791 bp DNA fragments, respectively, were expressed in Escherichia coli using the pET-20b(+) expression system. The His-Tag affinity purified VpChiA and VpChiAG589 enzymes had a calculated molecular mass of 65,713 and 62,723 Da, respectively. The results of biochemical characterization including kinetic parameters, spectroscopy of fluorescence and circular dichroism, chitin-binding and hydrolysis, and thermostability, both VpChiA and VpChiAG589, had very similar physicochemical properties such as the optimum pH (6), temperature (40 degrees C), and kinetic parameters of Km and kcat against the 4MU-(GlcNAc)(2) or 4MU-(GlcNAc)(3) soluble substrates. The significant increase of thermostability and the drastic decrease of the hydrolyzing ability of VpChiAG589 toward the insoluble alpha-chitin substrate suggested that a new role could be played by the C-terminal 30 amino acids.

Bacterial chitinases: properties and potential

Chitin is among the most abundant biomass present on Earth. Chitinase plays an important role in the decomposition of chitin and potentially in the utilization of chitin as a renewable resource. During the previous decade, chitinases have received increased attention because of their wide range of applications. Chito-oligomers produced by enzymatic hydrolysis of chitin have been of interest in recent years due to their broad applications in medical, agricultural, and industrial applications, including antibacterial, antifungal, hypocholesterolemic, and antihypertensive activity, and as a food quality enhancer. Microorganisms, particularly bacteria, form one of the major sources of chitinase. In this article, we have reviewed some of the chitinases produced by bacterial systems that have gained worldwide research interest for their diverse properties and potential industrial uses.

The dasABC gene cluster, adjacent to dasR, encodes a novel ABC transporter for the uptake of N,N'-diacetylchitobiose in Streptomyces coelicolor A3(2)

N,N'-Diacetylchitobiose [(GlcNAc)(2)] induces the transcription of chitinase (chi) genes in Streptomyces coelicolor A3(2). Physiological studies showed that (GlcNAc)(2) addition triggered chi expression and increased the rate of (GlcNAc)(2) concentration decline in culture supernatants of mycelia already cultivated with (GlcNAc)(2), suggesting that (GlcNAc)(2) induced the synthesis of its own uptake system. Four open reading frames (SCO0531, SCO0914, SCO2946, and SCO5232) encoding putative sugar-binding proteins of ABC transporters were found in the genome by probing the 12-bp repeat sequence required for regulation of chi transcription. SCO5232, named dasA, showed transcriptional induction by (GlcNAc)(2) and N,N',N'''-triacetylchitotriose [(GlcNAc)(3)]. Surface plasmon resonance analysis showed that recombinant DasA protein exhibited the highest affinity for (GlcNAc)(2) (equilibrium dissociation constant [K(D)] = 3.22 x 10(-8)). In the dasA-null mutant, the rate of decline of the (GlcNAc)(2) concentration in the culture supernatant was about 25% of that in strain M145. The in vitro and in vivo data clearly demonstrated that dasA is involved in (GlcNAc)(2) uptake. Upstream and downstream of dasA, the transcriptional regulator gene (dasR) and two putative integral membrane protein genes (dasBC) are located in the opposite and same orientations, respectively. The expression of dasR and dasB, which seemed independent of dasA transcription, was also induced by (GlcNAc)(2) and (GlcNAc)(3).

Conserved cis-Acting Elements Upstream of Genes Composing the Chitinolytic System of Streptomycetes Are DasR-Responsive Elements

For soil-dwelling bacteria that usually live in a carbon-rich and nitrogen-poor environment, the ability to utilize chitin - the second most abundant polysaccharide on earth - is a decisive evolving advantage as it is a source for both elements. Streptomycetes are high-GC Gram-positive soil bacteria that are equipped with a broad arsenal of chitinase-degrading genes. These genes are induced when the streptomycetes sense the presence of chitooligosaccharides. Their expression is repressed as soon as more readily assimilated carbon sources become available. This includes for example glucose or N-acetylglucosamine, the monomer subunit of chitin. Historically, the first cis-acting elements involved in carbon regulation in streptomycetes were found more than a decade ago upstream of chitinase genes, but the transcriptional regulator had so far remained undiscovered. In this work, we show that these cis-acting elements consist of inverted repeats with multiple occurrences and are bound by the HutC/GntR type regulator DasR. We have therefore designated these sites as DasR-responsive elements (dre). DasR, which is also the repressor of the genes for the N-acetylglucosamine-specific phosphotransferase transport system, should therefore play a critical role in sensing the balance between the monomeric and polymeric forms of N-acetylglucosamine.

Crystal structure and enzymatic properties of a bacterial family 19 chitinase reveal differences from plant enzymes

We describe the cloning, overexpression, purification, characterization and crystal structure of chitinase G, a single-domain family 19 chitinase from the Gram-positive bacterium Streptomyces coelicolor A3(2). Although chitinase G was not capable of releasing 4-methylumbelliferyl from artificial chitooligosaccharide substrates, it was capable of degrading longer chitooligosaccharides at rates similar to those observed for other chitinases. The enzyme was also capable of degrading a colored colloidal chitin substrate (carboxymethyl-chitin-remazol-brilliant violet) and a small, presumably amorphous, subfraction of alpha-chitin and beta-chitin, but was not capable of degrading crystalline chitin completely. The crystal structures of chitinase G and a related Streptomyces chitinase, chitinase C [Kezuka Y, Ohishi M, Itoh Y, Watanabe J, Mitsutomi M, Watanabe T & Nonaka T (2006) J Mol Biol358, 472-484], showed that these bacterial family 19 chitinases lack several loops that extend the substrate-binding grooves in family 19 chitinases from plants. In accordance with these structural features, detailed analysis of the degradation of chitooligosaccharides by chitinase G showed that the enzyme has only four subsites (- 2 to + 2), as opposed to six (- 3 to + 3) for plant enzymes. The most prominent structural difference leading to reduced size of the substrate-binding groove is the deletion of a 13-residue loop between the two putatively catalytic glutamates. The importance of these two residues for catalysis was confirmed by a site-directed mutagenesis study.

Biotechnological aspects of chitinolytic enzymes: a review

Chitin and chitinases (EC 3.2.1.14) have an immense potential. Chitinolytic enzymes have wide-ranging applications such as 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, and control of malaria transmission. In this review, we discuss the occurrence and structure of chitin, the types and sources of chitinases, their mode of action, chitinase production, as well as molecular cloning and protein engineering of chitinases and their biotechnological applications.

Enrichment of chitinolytic microorganisms: isolation and characterization of a chitinase exhibiting antifungal activity against phytopathogenic fungi from a novel Streptomyces strain

Thirteen different chitin-degrading bacteria were isolated from soil and sediment samples. Five of these strains (SGE2, SGE4, SSL3, MG1, and MG3) exhibited antifungal activity against phytopathogenic fungi. Analyses of the 16S rRNA genes and the substrate spectra revealed that the isolates belong to the genera Bacillus or Streptomyces. The closest relatives were Bacillus chitinolyticus (SGE2, SGE4, and SSL3), B. ehimensis (MG1), and Streptomyces griseus (MG3). The chitinases present in the culture supernatants of the five isolates revealed optimal activity between 45 degrees C and 50 degrees C and at pH values of 4 (SSL3), 5 (SGE2 and MG1), 6 (SGE4), and 5-7 (MG3). The crude chitinase preparations of all five strains possessed antifungal activity. The chitinase of MG3 (ChiIS) was studied further, since the crude enzyme conferred strong growth suppression of all fungi tested and was very active over the entire pH range tested. The chiIS gene was cloned and the gene product was purified. The deduced protein consisted of 303 amino acids with a predicted molecular mass of 31,836 Da. Sequence analysis revealed that ChiIS of MG3 is similar to chitinases of Streptomyces species, which belong to family 19 of glycosyl hydrolases. Purified ChiIS showed remarkable antifungal activity and stability.

Distribution and phylogenetic analysis of family 19 chitinases in Actinobacteria

In organisms other than higher plants, family 19 chitinase was first discovered in Streptomyces griseus HUT6037, and later, the general occurrence of this enzyme in Streptomyces species was demonstrated. In the present study, the distribution of family 19 chitinases in the class Actinobacteria and the phylogenetic relationship of Actinobacteria family 19 chitinases with family 19 chitinases of other organisms were investigated. Forty-nine strains were chosen to cover almost all the suborders of the class Actinobacteria, and chitinase production was examined. Of the 49 strains, 22 formed cleared zones on agar plates containing colloidal chitin and thus appeared to produce chitinases. These 22 chitinase-positive strains were subjected to Southern hybridization analysis by using a labeled DNA fragment corresponding to the catalytic domain of ChiC, and the presence of genes similar to chiC of S. griseus HUT6037 in at least 13 strains was suggested by the results. PCR amplification and sequencing of the DNA fragments corresponding to the major part of the catalytic domains of the family 19 chitinase genes confirmed the presence of family 19 chitinase genes in these 13 strains. The strains possessing family 19 chitinase genes belong to 6 of the 10 suborders in the order Actinomycetales, which account for the greatest part of the Actinobacteria: Phylogenetic analysis suggested that there is a close evolutionary relationship between family 19 chitinases found in Actinobacteria and plant class IV chitinases. The general occurrence of family 19 chitinase genes in Streptomycineae and the high sequence similarity among the genes found in Actinobacteria suggest that the family 19 chitinase gene was first acquired by an ancestor of the Streptomycineae and spread among the Actinobacteria through horizontal gene transfer.

Mutational analysis of the binding affinity and transport activity for N -acetylglucosamine of the novel ABC transporter Ngc in the chitin-degrader Streptomyces olivaceoviridis

The highly differentiated bacterium Streptomyces olivaceoviridis efficiently hydrolyses chitin, a highly abundant natural polysaccharide, to low molecular weight products including N-acetylglucosamine (NAG) and N,N' -diacetylchitobiose (chitobiose). NAG is taken up by a PTS (phosphoenolpyruvate-dependent phosphotransferase system) which includes the PtsC2 protein, and via the ABC (ATP-binding cassette) transporter Ngc, which itself includes the substrate-binding protein NgcE. This is at present the only ABC transporter which is known to mediate specific uptake of NAG (K(m) 0.48 microM, V(max) 1.3 nmol/min/mg dry weight) and is competitively inhibited by chitobiose (K(i) 0.68 microM). The latter finding suggests that the Ngc system transports both NAG and chitobiose efficiently. To identify amino acid residues required for the function of NgcE, either the wild-type or one of several mutant forms of the ngcE gene was introduced into the strain S. olivaceoviridis DeltaNgcE/DeltaPtsC1/DeltaPtsC2, which lacks both functional transport systems for NAG, and chromosomal recombinants were selected. Based on the in vivo transport parameters of the recombinants, and the in vitro binding characteristics of the corresponding purified proteins, the following conclusions can be drawn. (1) Replacement of the C-terminally located residue Y396 by A (Y396A) has little effect on ligand-binding or transport parameters. The W395A mutation also induced little change in the substrate affinity in vitro, but it led in vivo to a marked increase (11 fold) in K(m), and enhanced V(max) (by 1.5 fold). (2) The amino acids Y201 and W280 both contribute (51% and 38%) to the ligand-binding capacity of NgcE. They are both very important for the in vivo function of the complete transport apparatus; strains expressing either Y201A or W280A show drastically (100 or 150 times) enhanced K(m) values. (3) The concomitant presence of either Y200 and W280 or Y201 and W280 is essential for the function of NgcE. (4) Y201 is located within a tyrosyl-rich motif. This has been found to share some features with the ligand-binding site of amelogenins (enamel matrix proteins), which interact with NAG residues in glycoconjugates. In addition, it is distantly related to the ligand-binding site(s) in the plant-lectins UDA ( Urtica dioicaagglutinin, specific for NAG and its oligomers) and WGA (wheat germ agglutinin, which recognises a motif comprising three consecutive NAG residues).

Chitinase B of "Microbulbifer degradans" 2-40 contains two catalytic domains with different chitinolytic activities

Chitinase B of "Microbulbifer degradans" 2-40 is a modular protein that is predicted to contain two glycoside hydrolase family 18 (GH18) catalytic domains, two polyserine domains, and an acidic repeat domain. Each of the GH18 domains was shown to be catalytically active against chitin. Activity assays reveal that the amino-terminal catalytic domain (GH18(N)) releases methylumbelliferone from 4'-methylumbelliferyl-N,N'-diacetylchitobiose 13.6-fold faster than the carboxy-terminal catalytic domain (GH18(C)) and releases chitobiose from the nonreducing end of chitooligosaccharides, therefore functioning as an exochitinase. GH18(C) releases methylumbelliferone from 4'-methylumbelliferyl-N,N',N"-triacetylchitotriose 2.7-fold faster than GH18(N) and cleaves chitooligosaccharides at multiple bonds, consistent with endochitinolytic activity. Each domain was maximally active from 30 to 37 degrees C and from pH 7.2 to 8.0 and was not affected by Mg(2+), Mn(2+), Ca(2+), K(+), EDTA, EGTA, or 1.0 M NaCl. The activity of each domain was moderately inhibited by Ni(2+), Sr(2+), and Cu(2+), while Hg(2+) completely abolished activity. When the specific activities of various recombinant portions of ChiB were calculated by using native chitin as a substrate, the polypeptide containing the endo-acting domain was twofold more active on native chitin than the other containing the exo-acting domain. The presence of both domains in a single reaction increased the amount of reducing sugars released from native chitin to 140% above the theoretical combined rate, indicating that the domains function cooperatively to degrade chitin. These data demonstrate that the GH18 domains of ChiB have different activities on the same substrate and function cooperatively to enhance chitin depolymerization.

The phosphotransferase system of Streptomyces coelicolor is biased for N-acetylglucosamine metabolism

Mutation of the crr-ptsI gene locus revealed that Streptomyces coelicolor uses the phosphotransferase system (PTS) for N-acetylglucosamine uptake. crr, ptsI, and ptsH, which encode the three general PTS phosphotransferases, are induced by N-acetylglucosamine but not by other PTS substrates. Thus, the S. coelicolor PTS is biased for N-acetylglucosamine utilization, a novel feature that distinguishes this PTS from others.

Characterization of chitinase genes from an alkaliphilic actinomycete, Nocardiopsis prasina OPC-131

An alkaliphilic actinomycete, Nocardiopsis prasina OPC-131, secretes chitinases, ChiA, ChiB, and ChiB Delta, in the presence of chitin. The genes encoding ChiA and ChiB were cloned and sequenced. The open reading frame (ORF) of chiA encoded a protein of 336 amino acids with a calculated molecular mass of 35,257 Da. ChiA consisted of only a catalytic domain and showed a significant homology with family 18 chitinases. The chiB ORF encoded a protein of 296 amino acids with a calculated molecular mass of 31,500 Da. ChiB is a modular enzyme consisting of a chitin-binding domain type 3 (ChtBD type 3) and a catalytic domain. The catalytic domain of ChiB showed significant similarity to Streptomyces family 19 chitinases. ChiB Delta was the truncated form of ChiB lacking ChtBD type 3. Expression plasmids coding for ChiA, ChiB, and ChiB Delta were constructed to investigate the biochemical properties of these recombinant proteins. These enzymes showed pHs and temperature optima similar to those of native enzymes. ChiB showed more efficient hydrolysis of chitin and stronger antifungal activity than ChiB Delta, indicating that the ChtBD type 3 of ChiB plays an important role in the efficient hydrolysis of chitin and in antifungal activity. Furthermore, the finding of family 19 chitinase in N. prasina OPC-131 suggests that family 19 chitinases are distributed widely in actinomycetes other than the genus Streptomyces.

Molecular analysis of a bacterial chitinolytic community in an upland pasture

The effects of agricultural-improvement treatments on the chitinolytic activity and diversity of a microbial community were investigated within an upland pasture. The treatments of interest were lime and treated sewage sludge, both commonly applied to pasture land to improve fertility. Burial of chitin-containing litter bags at the field site resulted in enrichment of bacteria according to 16S rRNA fingerprinting. Chitinolytic-activity measurements showed that the highest activity occurred in those bags recovered from sludge-amended plots, which correlated well with increased counts of actinobacteria in samples from these chitin bags. Our findings suggest that sewage sludge increases the fertility of the soil in terms of chitinase activity. Ten clone libraries were constructed from family 18 subgroup A chitinases, PCR amplified from litter bags buried in soil in July 2000 or in September 2000, in a separate study. Analysis of these libraries by restriction fragment length polymorphism and sequencing showed that they were dominated by actinobacterium-like chitinase sequences. This suggests that actinobacteria have an important chitinolytic function in this soil ecosystem. Our findings showed that sludge application increased chitinolytic activity but decreased the diversity of chitinases present.

Chitinases A, B, and C1 of Serratia marcescens 2170 produced by recombinant Escherichia coli: enzymatic properties and synergism on chitin degradation

To discover the individual roles of the chitinases from Serratia marcescens 2170, chitinases A, B, and C1 (ChiA, ChiB, and ChiC1) were produced by Escherichia coli and their enzymatic properties as well as synergistic effect on chitin degradation were studied. All three chitinases showed a broad pH optimum and maintained significant chitinolytic activity between pH 4 and 10. ChiA was the most active enzyme toward insoluble chitins, but ChiC1 was the most active toward soluble chitin derivatives among the three chitinases. Although all three chitinases released (GlcNAc)2 almost exclusively from colloidal chitin, ChiB and ChiC1 split (GlcNAc)6 to (GlcNAc)3, while ChiA exclusively generated (GlcNAc)2 and (GlcNAc)4. Clear synergism on the hydrolysis of powdered chitin was observed in the combination between ChiA and either ChiB or ChiC, and the sites attacked by ChiA on the substrate are suggested to be different from those by either ChiB or ChiC1.

Response regulator ChiR regulates expression of chitinase gene, chiC, in Streptomyces coelicolor

Transcription from the chiC promoter, directing expression of the chitinase gene, chiC, in Streptomyces coelicolor, was analyzed using xylE reporter gene and high-resolution S1-nuclease mapping. The transcription from the chiC promoter was induced by chitin, and this induction was dramatically reduced in the S. coelicolor chiR-disrupted strain. This indicated a dependence of chiC expression upon the chiR gene encoding a response regulator protein. To investigate this relationship, the S. coelicolor ChiR was overproduced using Escherichia coli T7 RNA polymerase expression system. However, gel mobility shift-assay with such a purified ChiR showed no binding in the chiC promoter region, which indicates a lack of specific phosphorylation of E. coli overproduced ChiR that is necessary for DNA-binding activity of response regulators.

Cloning and sequencing of two genes encoding chitinases A and B from Bacillus cereus CH

Two genes encoding chitinases A and B (chiA and chiB) from Bacillus cereus CH were cloned into Escherichia coli XL1-Blue MRF' by using pBluescript II SK+, and their nucleotide sequences were determined. Open reading frames of the chiA and chiB genes encoded distinct polypeptide chains consisting of 360 and 674 amino acid residues, respectively, with calculated molecular sizes of 39 470 and 74 261 Da, respectively. Comparison of the deduced amino acid sequences with those of other bacterial chitinases revealed that chitinase A consisted of a catalytic domain, while chitinase B consisted of three functional domains, a catalytic domain, a fibronectin type III-like domain, and a cellulose-binding domain. The primary structures of these two proteins were not similar to each other.Key words: Bacillus cereus, chitinase, cloning.

A Bacillus amyloliquefaciens ChbB protein binds beta- and alpha-chitin and has homologues in related strains

A small (19.8 kDa) protein was identified in Bacillus amyloliquefaciens ALKO 2718 cultures during growth in the presence of yeast extract and chitin, but not with glucose. The protein targets beta-chitin best, then alpha-chitin, but barely any other polysaccharide. This described chitin-binding protein (ChbB) is the first of its type from a Bacillus strain and cross-reacts with antibodies raised against the Streptomyces alpha-chitin-binding protein CHB1. Using reverse genetics, the chromosomal chbB gene of strain ALKO 2718 was identified, cloned and sequenced. ChbB shares several motifs with the alpha-chitin-binding proteins CHB1 and CHB2 of Streptomyces and CBP21 of Serratia marcescens predominantly targeting beta-chitin. Synthesis was repressed by glucose and the presence of cre boxes suggests catabolite control. Using PCR, Southern hybridization and anti-ChbB antibodies, the presence of a chbB gene, as well as of a ChbB protein homologue, was ascertained in several tested B. amyloliquefaciens strains, but not in Bacillus subtilis 168. Contrary to B. subtilis 168, all B. amyloliquefaciens strains secreted varying amounts of enzymic activity, degrading carboxymethyl chitin coupled with Remazol brilliant violet.

Purification and characterization of a chitinase from Trichoderma viride

Usukizyme, a commercial enzyme preparation from Trichoderma viride, showed multiple chitin- degrading activities. One of these was purified to homogeneity by sequential DEAE Sepharose CL-6B, Q-Sepharose FF, and Sephacryl S-100 HR column chromatographies. The purified enzyme showed optimum activity at pH 3.5 and 50 degrees -55 degrees C and was stable in the pH range of 3.5-6.0 and up to 45 degrees C. It showed higher activity toward chitosan-7B, a 62% deacetylated chitosan, as opposed to highly deacetylated chitosan substrates. Products of degradation of a 1% (w/v) solution of partially deacetylated chitin (PC-100) were purified on CM-Sephadex C-25 and analyzed by HPLC, exo-glycosidase digestion, and nitrous acid deamination. The enzyme was unable to split the GlcN-GlcN linkages in the substrate. It produced mainly (GlcNAc)(2) and (GlcNAc)(3) along with mixed oligosaccharides. When subjected to nitrous acid degradation, some of the mixed oligosaccharides produced mainly 2-deoxyglucitol, implying the presence of GlcN at the reducing end of the oligosaccharides.

Characteristics of a Streptomyces coelicolor A3(2) extracellular protein targeting chitin and chitosan

Upstream of the Streptomyces coelicolor A3(2) chitinase G gene, a small gene (named chb3) is located whose deduced product shares 37% identical amino acids with the previously described CHB1 protein from Streptomyces olivaceoviridis. The chb3 gene and its upstream region were cloned in a multicopy vector and transformed into the plasmid-free Streptomyces lividans TK21 strain. The CHB3 protein (14.9 kDa) was secreted by the S. lividans TK21 transformant during growth in the presence of glucose, N-acetylglucosamine, yeast extract, and chitin. The protein was purified to homogeneity using anionic exchange, hydrophobic interaction chromatographies, and gel filtration. In contrast to CHB1, CHB3 targets alpha-chitin, beta-chitin, and chitosan at pH 6.0 but does so relatively loosely. The ecological implications of the divergence of substrate specificity of various types of chitin-binding proteins are described.

Purification, cloning, and DNA sequence analysis of a chitinase from an overproducing mutant of Streptomyces peucetius defective in daunorubicin biosynthesis

Extracellular chitinases of Streptomyces peucetius and a chitinase overproducing mutant, SPVI, were purified to homogeneity by ion exchange and gel filtration chromatography. The purified enzyme has a molecular mass of 42 kDa on SDS-PAGE, and the N-terminal amino acid sequence of the protein from the wild type showed homology to catalytic domains (Domain IV) of several other Streptomyces chitinases such as S. lividans 66, S. coelicolor A3(2), S. plicatus, and S. thermoviolaceus OPC-520. Purified SPVI chitinase cross-reacted to anti-chitinase antibodies of wild-type S. peucetius chitinase. A genomic library of SPVI constructed in E. coli using λ DASH II was probed with chiC of S. lividans 66 to screen for the chitinase gene. A 2.7 kb fragment containing the chitinase gene was subcloned from a λ DASH II clone, and sequenced. The deduced protein had a molecular mass of 68 kDa, and showed domain organization similar to that of S. lividans 66 chiC. The N-terminal amino acid sequence of the purified S. peucetius chitinase matched with the N-terminus of the catalytic domain, indicating the proteolytic processing of 68 kDa chitinase precursor protein to 42 kDa mature chitinase containing the catalytic domain only. A putative chiR sequence of a two-component regulatory system was found upstream of the chiC sequence.Key words: chitinase, chitinase purification, Streptomyces peucetius, daunorubicin, chiC.

Transcriptional co-regulation of five chitinase genes scattered on the Streptomyces coelicolor A3(2) chromosome

Streptomyces coelicolor A3(2) strain M145 has eight chitinase genes scattered on the chromosome: six genes for family 18 (chiA, B, C, D, E and H) and two for family 19 (chiF and G). In this study, the expression and regulation of these genes were investigated. The transcription of five of the genes (chiA, B, C, D and F) was induced in the presence of colloidal chitin while that of the other three genes (chiE, G and H) was not. The transcripts of the five induced chi genes increased and reached their maximum at 4 h after the addition of colloidal chitin, all showing the same temporal patterns. The induced levels of the transcripts of chiB were significantly lower than those of the other four genes. Dynamic analysis of the transcripts of the chi genes indicated that chiA and chiC were induced more strongly than chiD and chiF. Addition of chitobiose also induced transcription of the chi genes, but significantly earlier than did colloidal chitin. When cells were cultured in the presence of colloidal chitin, an exponential increase of chitobiose concentration in the culture supernatant was observed prior to the induced transcription of the chi genes. This result, together with the immediate effect of chitobiose on the induction, suggests that chitobiose produced from colloidal chitin is involved in the induction of transcription of the chi genes. The transcription of the five chi genes was repressed by glucose. This repression was apparently mediated by the glucose kinase gene glkA.

Isolation of a chitinase overproducing mutant of Streptomyces peucetius defective in daunorubicin biosynthesis

Streptomyces peucetius, producer of the antitumor anthracycline antibiotic daunorubicin, was mutagenized, and mutants defective in daunorubicin biosynthesis were screened. One mutant (SPVI), which failed to produce daunorubicin, was found to overproduce an extracellular chitinase. Time course analyses of chitinase production and of the extracellular protein profile showed that the increase in activity is due to increased synthesis of the enzyme protein. The production of chitinase in SPVI was repressed by glucose as in the case of wild-type S. peucetius. PFGE analysis of VspI restriction fragments of S. peucetius and SPVI showed that there was no major alteration in the mutant genome. The hybridization pattern of S. peucetius and SPVI genomic DNA digested with various restriction enzymes was identical when probed with dnrUVJI genes of the S. peucetius daunorubicin cluster and chiA of Streptomyces lividans 66. The possible step affected in the daunorubicin biosynthetic pathway could be a polyketide synthase, since aklanonic acid, the earliest detectable intermediate in the daunorubicin pathway, was not synthesized in SPVI.Key words: Streptomyces peucetius, chitinase, daunorubicin, NTG mutagenesis.

Identification of DNA amplifications near the center of the Streptomyces coelicolor M145 chromosome

Linear streptomycete chromosomes frequently undergo spontaneous gross DNA rearrangements at the terminal regions. Large DNA deletions of the chromosome ends are in many cases associated with tandemly reiterated DNA amplifications, found at the border of the deletable areas. In contrast to previous reports, we have discovered amplifications near the center of the Streptomyces coelicolor M145 chromosome. The detected amplified units of DNA are 19.9 kb and 16 kb in length and exist in copy numbers of 30 and 40, respectively. Both amplifications were located in the same region and share at least 3.6 kb.