Biochemical Characterization of a Novel Acidic Exochitinase from Rhizomucor miehei with Antifungal Activity

Response surface optimization, purification, characterization and short-chain chitooligosaccharides production from an acidic, thermostable chitinase from Thermomyces dupontii

Chitin, recovered in huge amounts from coastal waste, may biocatalytically valorized for utilization in food and biotech sectors. Conventional chemical-based conversion makes use of significant volumes of hazardous acid and alkali. Alternatively, enzymes offer better process control and generation of homogeneous products. Process variables were derived to achieve augmented levels of chitinase (3.8809 Ul-1 h-1) productivity from a novel thermophilic fungal strain Thermomyces dupontii, ITCC 9104 following incubation (96 h, 45 °C). An acidic thermostable chitinase TdChiT having molecular mass of 60 kDa has been purified. Optimal TdChiT activity has been demonstrated at 70 °C and pH 5. Notably decreased activity over a broad range of temperature and pH was observed following deglycosylation. Half-life, activation energy, Gibbs free energy, enthalpy and entropy for denaturation of TdChiT at its optimum temperature were 197.40 min, 105.48 kJ mol-1, 100.59 kJ mol-1, 102.64 kJ mol-1 and 5.95 J mol-1 K-1. TdChiT has specificity towards colloidal chitin and (GlcNAc)2-4. Metal ions viz. Mn2+, Ca2+ and Co2+ and nonionic surfactants notably enhanced chitinase activity. Thin layer chromatography analysis has revealed effective hydrolysis of colloidal chitin and (GlcNAc)2-4. TdChiT may potentially be employed for design of better, eco-friendly and less resource-intensive industrial procedures for upcycling of crustacean waste into value-added organonitrogens.

Marine enzymes: Classification and application in various industries

Oceans are regarded as a plentiful and sustainable source of biological compounds. Enzymes are a group of marine biomaterials that have recently drawn more attention because they are produced in harsh environmental conditions such as high salinity, extensive pH, a wide temperature range, and high pressure. Hence, marine-derived enzymes are capable of exhibiting remarkable properties due to their unique composition. In this review, we overviewed and discussed characteristics of marine enzymes as well as the sources of marine enzymes, ranging from primitive organisms to vertebrates, and presented the importance, advantages, and challenges of using marine enzymes with a summary of their applications in a variety of industries. Current biotechnological advancements need the study of novel marine enzymes that could be applied in a variety of ways. Resources of marine enzyme can benefit greatly for biotechnological applications duo to their biocompatible, ecofriendly and high effectiveness. It is beneficial to use the unique characteristics offered by marine enzymes to either develop new processes and products or improve existing ones. As a result, marine-derived enzymes have promising potential and are an excellent candidate for a variety of biotechnology applications and a future rise in the use of marine enzymes is to be anticipated.

Chitinase-Assisted Bioconversion of Chitinous Waste for Development of Value-Added Chito-Oligosaccharides Products

Chito-oligosaccharides (COSs) are the partially hydrolyzed products of chitin, which is abundant in the shells of crustaceans, the cuticles of insects, and the cell walls of fungi. These oligosaccharides have received immense interest in the last few decades due to their highly promising bioactivities, such as their anti-microbial, anti-tumor, and anti-inflammatory properties. Regarding environmental concerns, COSs are obtained by enzymatic hydrolysis by chitinase under milder conditions compared to the typical chemical degradation. This review provides updated information about research on new chitinase derived from various sources, including bacteria, fungi, plants, and animals, employed for the efficient production of COSs. The route to industrialization of these chitinases and COS products is also described.

Characterization of Chitinolytic and Antifungal Activities in Marine-Derived Trichoderma bissettii Strains

Trichoderma fungi have been intensively studied for mycoparasitism, and the latter is closely related to their cell-wall degrading enzymes including chitinase. Here, we studied marine-derived Trichoderma spp., isolated from distinct sources and locations, for chitinolytic and antifungal activity. Based on morphological and phylogenetic analyses, two strains designated GJ-Sp1 and TOP-Co8 (isolated from a marine sponge and a marine alga, respectively) were identified as Trichoderma bissettii. This species has recently been identified as a closely related species to Trichoderma longibrachiatum. The extracellular crude enzymes of GJ-Sp1 and TOP-Co8 showed activities of chitobiosidase and β-N-acetylglucosaminidase (exochitinase) and chitotriosidase (endochitinase). The optimum chitinolytic activity of the crude enzymes was observed at 50 °C, pH 5.0, 0-0.5% NaCl concentrations, and the activities were stable at temperatures ranging from 10 to 40 °C for 2 h. Moreover, the crude enzymes showed inhibitory activity against hyphal growth of two filamentous fungi Aspergillus flavus and Aspergillus niger. To the best of our knowledge, this is the first report of the chitinolytic and antifungal activity of T. bissettii.

The Discovery, Enzymatic Characterization and Functional Analysis of a Newly Isolated Chitinase from Marine-Derived Fungus Aspergillus fumigatus df347

In order to discover a broad-specificity and high stability chitinase, a marine fungus, Aspergillus fumigatus df347, was identified in the sediments of mangrove wetlands in Qinzhou Bay, China. The chitinase gene (AfChi28) from A. fumigatus df347 was cloned and heterologously expressed in Escherichia coli, and the recombinant enzyme AfChi28 was purified and characterized. AfChi28 is an acido-halotolerant- and temperature-resistant bifunctional enzyme with both endo- and exo-cleavage functions. Its enzymatic products are mainly GlcNAc, (GlcNAc)2, (GlcNAc)3 and (GlcNAc)4. Na+, Mg2+, K+, Ca2+ and Tris at a concentration of 50 mM had a strong stimulatory effect on AfChi28. The crude enzyme and pure enzyme exhibited the highest specific activity of 0.737 mU/mg and 52.414 mU/mg towards colloidal chitin. The DxDxE motif at the end of strand β5 and with Glu154 as the catalytic residue was verified by the AlphaFold2 prediction and sequence alignment of homologous proteins. Moreover, the results of molecular docking showed that molecular modeling of chitohexaose was shown to bind to AfChi28 in subsites −4 to +2 in the deep groove substrate-binding pocket. This study demonstrates that AfChi28 is a promising chitinase for the preparation of desirable chitin oligosaccharides, and provides a foundation for elucidating the catalytic mechanism of chitinases from marine fungi.

A Contemporary Appraisal on Impending Industrial and Agricultural Applications of Thermophilic-Recombinant Chitinolytic Enzymes from Microbial Sources

The ability of chitinases to degrade the second most abundant polymer, chitin, into potentially useful chitooligomers and chitin derivatives has not only rendered them fit for chitinous waste management but has also made them important from industrial point of view. At the same time, they have also been recognized to have an imperative role as promising biocontrol agents for controlling plant diseases. As thermostability is an important property for an industrially important enzyme, various bacterial and fungal sources are being exploited to obtain such stable enzymes. These stable enzymes can also play a role in agriculture by maintaining their stability under adverse environmental conditions for longer time duration when used as biocontrol agent. Biotechnology has also played its role in the development of recombinant chitinases with enhanced activity, thermostability, fungicidal and insecticidal activity via recombinant DNA techniques. Furthermore, a relatively new approach of generating pathogen-resistant transgenic plants has opened new ways for sustainable agriculture by minimizing the yield loss of valuable crops and plants. This review focuses on the potential applications of thermostable and recombinant microbial chitinases in industry and agriculture.

Effectors with chitinase activity (EWCAs), a family of conserved, secreted fungal chitinases that suppress chitin-triggered immunity

In plants, chitin-triggered immunity is one of the first lines of defense against fungi, but phytopathogenic fungi have developed different strategies to prevent the recognition of chitin. Obligate biotrophs such as powdery mildew fungi suppress the activation of host responses; however, little is known about how these fungi subvert the immunity elicited by chitin. During epiphytic growth, the cucurbit powdery mildew fungus Podosphaera xanthii expresses a family of candidate effector genes comprising nine members with an unknown function. In this work, we examine the role of these candidates in the infection of melon (Cucumis melo L.) plants, using gene expression analysis, RNAi silencing assays, protein modeling and protein-ligand predictions, enzymatic assays, and protein localization studies. Our results show that these proteins are chitinases that are released at pathogen penetration sites to break down immunogenic chitin oligomers, thus preventing the activation of chitin-triggered immunity. In addition, these effectors, designated effectors with chitinase activity (EWCAs), are widely distributed in pathogenic fungi. Our findings reveal a mechanism by which fungi suppress plant immunity and reinforce the idea that preventing the perception of chitin by the host is mandatory for survival and development of fungi in plant environments.

Biochemical characterization of a novel acidic chitinase with antifungal activity from Paenibacillus xylanexedens Z2-4

A chitinase gene (PxChi52) from Paenibacillus xylanexedens Z2-4 was cloned and heterologously expressed in Escherichia coli BL21 (DE3). PxChi52 shared the highest identity of 91% with a glycoside hydrolase family 18 chitinase (ChiD) from Bacillus circulans. The recombinant enzyme (PxChi52) was purified and biochemically characterized. PxChi52 had a molecular mass of 52.8 kDa. It was most active at pH 4.5 and 65 °C, respectively, and stable in a wide pH range of 4.0-13.0 and up to 50 °C. The enzyme exhibited the highest specific activity of 16.0 U/mg towards colloidal chitin, followed by ethylene glycol chitin (5.4 U/mg) and ball milled chitin (0.4 U/mg). The K_m and V_max values of PxChi52 towards colloidal chitin were determined to be 3.06 mg/mL and 71.38 U/mg, respectively, PxChi52 hydrolyzed colloidal chitin and chitooligosaccharides with degree of polymerization 2-5 to release mainly N-acetyl chitobiose. In addition, PxChi52 displayed inhibition effects on the growth of some phytopathogenic fungi, including Alternaria alstroemeriae, Botrytis cinerea, Rhizoctonia solani, Sclerotinia sclerotiorum and Valsa mali. The unique properties of PxChi52 may enable it potential application in agriculture field as a biocontrol agent.

Production of Structurally Defined Chito-Oligosaccharides with a Single N-Acetylation at Their Reducing End Using a Newly Discovered Chitinase from Paenibacillus pabuli

Partially acetylated chito-oligosaccharides (paCOSs) are bioactive compounds with potential medical applications. Their biological activities are largely dependent on their structural properties, in particular their degree of polymerization (DP) and the position of the acetyl groups along the glycan chain. The production of structurally defined paCOSs in a purified form is highly desirable to better understand the structure/bioactivity relationship of these oligosaccharides. Here, we describe a newly discovered chitinase from Paenibacillus pabuli (PpChi) and demonstrate by mass spectrometry that it essentially produces paCOSs with a DP of three and four that carry a single N-acetylation at their reducing end. We propose that this specific composition of glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) residues, as in GlcN_(n)GlcNAc₁, is due to a subsite specificity toward GlcN residues at the -2, -3, and -4 positions of the partially acetylated chitosan substrates. In addition, the enzyme is stable, as evidenced by its long shelf life, and active over a large temperature range, which is of high interest for potential use in industrial processes. It exhibits a k_cat of 67.2 s^-1 on partially acetylated chitosan substrates. When PpChi was used in combination with a recently discovered fungal auxilary activity (AA11) oxidase, a sixfold increase in the release of oligosaccharides from the lobster shell was measured. PpChi represents an attractive biocatalyst for the green production of highly valuable paCOSs with a well-defined structure and the expansion of the relatively small library of chito-oligosaccharides currently available.

A thermophilic chitinase 1602 from the marine bacterium Microbulbifer sp. BN3 and its high-level expression in Pichia pastoris

Chitinases play an important role in many industrial processes, including the preparation of oligosaccharides with potential applications. In the present study, a 1,713 bp gene of Chi1602, derived from a marine bacterium Microbulbifer sp. BN3, encoding a GH18 family chitinase, was expressed at high levels in Pichia pastoris. Distinct from most of the marine chitinases, the recombinant chitinase 1602 exhibited maximal activity at 60 °C and over a broad pH range between 5.0 and 9.0, and was stable at 50 °C and over the pH range 4.0-9.0. The hydrolytic products derived from colloidal chitins comprised mainly (GlcNAc)₂ and GlcNAc, indicating that rChi1602 is a GH18 processive chitinase in conformity with its hypothetical structure. However, rChi1602 showed traces of β-N-acetylglucosaminidase activity on substrates such as powder chitin, chitosan, and ethylene glycol chitin. The thermophilic rChi1602, which manifests adaptation to a wide pH range and can be expressed at a high level in P. pastoris, is advantageous for applications in industrial processes.

Expression and biochemical characterization of a novel chitinase ChiT-7 from the metagenome in the soil of a mangrove tidal flat in China

Chitinases play an important role in the process of chitin bioavailability. In this study, we cloned a new chitinase gene and characterized its recombinant protein. The new 1251 bp gene of chitinase (ChiT-7) was cloned from the metagenome of the mangrove tidal flat soil in the city of Zhangzhou in Fujian Province (China) by genome walking. The gene encoded a mature protein with 381 amino acids, which manifested certain sequence similarity (59% identity) to characterized GH18 chitinases. The mature protein of ChiT-7 was successfully expressed in E. coli BL21 (DE3). After purification, the specific activity of the recombinant enzyme was 0.63 U/mg at the optimal pH of 6.0 and the optimal temperature of 45 °C. The rChiT-7 was active over a wide pH range, and the residual enzyme activity reached 80% or higher at 30 °C-50 °C. rChiT-7 hydrolyzed colloidal chitin with (GlcNAc)2 and GlcNAc as the main final products. Structural analysis of ChiT-7 indicated that ChiT-7 could be a processive chitinase. rChiT-7 manifested characteristics analogous to those of fungi and actinomycetes and exhibited sequence homology.

Characterization of a GH Family 20 Exo-β-N-acetylhexosaminidase with Antifungal Activity from Streptomyces avermitilis

We characterized SaHEX, which is a glycoside hydrolase (GH) family 20 exo-β-N-acetylhexosaminidase found in Streptomyces avermitilis. SaHEX exolytically hydrolyzed chitin oligosaccharides from their non-reducing ends, and yielded N-acetylglucosamine (GlcNAc) as the end product. According to the initial rate of substrate hydrolysis, the rates of (GlcNAc)₃ and (GlcNAc)₅ hydrolysis were greater than the rates for the other oligosaccharides. The enzyme exhibited antifungal activity against Aspergillus niger, which was probably due to hydrolytic activity with regard to chitin in the hyphal tips. Therefore, SaHEX has potential for use in GlcNAc production and food preservation.

Identification and characterization of a marine-derived chitinolytic fungus, Acremonium sp. YS2-2

Chitin is the most abundant biopolymer in marine environments. To facilitate its utilization, our laboratory screened marine-derived fungal strains for chitinolytic activity. One chitinolytic strain isolated from seawater, designated YS2-2, was identified as Acremonium species based on morphological and phylogenetic analyses. Acremonium species are cosmopolitan fungi commonly isolated from both terrestrial and marine environments, but their chitinolytic activity is largely unknown. The extracellular crude enzyme of YS2-2 exhibited optimum chitinolytic activity at pH 6.0-7.6, 23-45°C, and 1.5% (w/v) NaCl. Degenerate PCR revealed the partial cDNA sequence of a putative chitinase gene, chiA, in YS2-2. The expression of chiA was dramatically induced in response to 1% (w/v) colloidal chitin compared to levels under starvation, chitin powder, and glucose conditions. Moreover, the chiA transcript levels were positively correlated with chitinolytic activities under various colloidal chitin concentrations, suggesting that ChiA mediates chitinolytic activity in this strain. Our results provide a basis for additional studies of marinederived chitinolytic fungi aimed at improving industrial applications.

Intergeneric fusant development using chitinase preparation of Rhizopus stolonifer NCIM 880

Fungal chitinase have tremendous applications in biotech industries, with this approach we focused on extracellular chitinase from Rhizopus stolonifer NCIM 880 for the formation of fungal protoplasts. The maximum chitinase production reached after 24 h at 2.5% colloidal chitin concentration in presence of starch as an inducer. Chitinase was extracted efficiently at 65% cold acetone concentration and then purified by using DEAE-Cellulose column chromatography. Purified chitinase having molecular weight 22 kDa with single polypeptide chain was optimally active at pH 5.0 and temperature 30 °C. The purified chitinase revealed kinetic properties like Km 1.66 mg/ml and Vmax 769 mM/min. Crude chitinase extract efficiently formed protoplasts from A. niger, A. oryzae, T. viride and F. moniliforme. The formed protoplasts of A. niger and T. viride showed 70 and 66% regeneration frequency respectively. Further, intergeneric fusants were developed successfully and identified at molecular level using RNA profiling. Thus, this study could be useful for strain improvement of various fungi for biotechnological applications.

Enhancement of Exochitinase Production by Bacillus licheniformis AT6 Strain and Improvement of N-Acetylglucosamine Production

A strain producing chitinase, isolated from potato stem tissue, was identified as Bacillus licheniformis by biochemical properties and 16S RNA sequence analysis. Statistical experimental designs were used to optimize nine independent variables for chitinase production by B. licheniformis AT6 strain in submerged fermentation. Using Plackett-Burman design, (NH₄)₂SO₄, MgSO₄.7H₂O, colloidal chitin, MnCl₂ 2H₂O, and temperature were found to influence chitinase production significantly. According to Box-Behnken response surface methodology, the optimal fermentation conditions allowing maximum chitinase production were (in gram per liter): (NH₄)₂SO₄, 7; K₂HPO₄, 1; NaCl, 1; MgSO₄.7H₂O, 0.1; yeast extract, 0.5; colloidal chitin, 7.5; MnCl₂.2H₂O, 0.2; temperature 35 °C; pH medium 7. The optimization strategy led to a 10-fold increase in chitinase activity (505.26 ± 22.223 mU/mL versus 50.35 ± 19.62 mU/mL for control basal medium). A major protein band with a molecular weight of 61.9 kDa corresponding to chitinase activity was clearly detected under optimized conditions. Chitinase activity produced in optimized medium mainly releases N-acetyl glucosamine (GlcNAc) monomer from colloidal chitin. This enzyme also acts as an exochitinase with β-N-acetylglucosaminidase. These results suggest that B. licheniformis AT6 secreting exochitinase is highly efficient in GlcNAc production which could in turn be envisaged as a therapeutic agent or as a conservator against the alteration of several ailments.