Potent Fungal Chitinase for the Bioconversion of Mycelial Waste

Biochemical Characterization of a Family GH18 Specific-Domain Chitinase: Chitin-Binding Domain Modulates the Reaction Specificity

Chitinase is an essential tool for the high-value utilization of chitin and the production of N-acetyl chito-oligosaccharides (N-acetyl COSs). The reaction specificity of chitinase is a key determinant of product composition. Previous studies have shown that carbohydrate-binding modules (CBMs) may influence the reaction specificity of glycoside hydrolases, though few studies have focused on this aspect in chitinases. Here, we identified a chitinase ChiZg from Zooshikella ganghwensis, characterized by the spatial separation of the chitin-binding domain (ChBD) from the catalytic domain (CD). ChiZg modulated product specificity for (GlcNAc)2 in an atypical exo-mode, and the (GlcNAc)2 yield ultimately maintained a relative balance as the substrate concentration and enzyme amount changed. Additionally, we found that the ChBD in ChiZg could modulate the enzyme's reaction specificity. A ChBD-truncated mutant exhibited additional N-acetylglucosaminidase activity, hydrolyzing (GlcNAc)2 to GlcNAc. We also engineered a mutant by translocating the ChBD from the N-terminus to the C-terminus, which aligned with the CD spatial configuration. It enhanced product specificity for (GlcNAc)3 with minimal GlcNAc production. This work expands the understanding of the ChBD-mediated reaction specificity in chitinases, providing an effective catalytic tool for the efficient degradation of chitin and the production of N-acetyl COSs with specific configurations.

Identification, expression, and characterization of a marine-derived chitinase Ce0303 from Chitiniphilus eburneus YS-30 with exo- and endo-hydrolytic properties

N-acetyl-oligosaccharides exhibit antioxidant and antibacterial activities. However, the low catalytic efficiency of chitinase on crystalline chitin hinders the eco-friendly production of N-acetyl-oligosaccharides. A marine-derived chitinase-producing strain Chitiniphilus eburneus YS-30 was screened in this study. The genome of C. eburneus YS-30 spans 4,522,240 bp, with a G + C content of 63.96 % and 4244 coding genes. Among the chitinases secreted by C. eburneus YS-30, Ce0303 showed the highest content at 19.10 %, with a molecular weight of 73.5 kDa. Recombinant Ce0303 exhibited optimal activity at 50 °C and pH 5.0, maintaining stability across pH 4.0-10.0. Ce0303 demonstrated strict substrate specificity, with a specific activity toward colloidal chitin of 6.41 U mg-1, Km of 2.34 mg mL-1, and kcat of 3.27 s-1. The specific activity of Ce0303 toward α-chitin was 18.87 % of its activity on colloidal chitin. Ce0303 displayed both exo- and endo-hydrolytic properties, primarily producing (GlcNAc)1-3 from colloidal chitin. The structure of Ce0303 includes one catalytic domain and two chitin-binding domains. Docking results revealed that the GlcNAc at -1 subsite formed two hydrogen bonds with conserved Trp380. The hydrolytic properties of Ce0303 will provide technical support for the comprehensive utilization of crustacean raw materials.

Three-Step Enzymatic Remodeling of Chitin into Bioactive Chitooligomers

Here we describe a complex enzymatic approach to the efficient transformation of abundant waste chitin, a byproduct of the food industry, into valuable chitooligomers with a degree of polymerization (DP) ranging from 6 to 11. This method involves a three-step process: initial hydrolysis of chitin using engineered variants of a novel fungal chitinase from Talaromyces flavus to generate low-DP chitooligomers, followed by an extension to the desired DP using the high-yielding Y445N variant of β-N-acetylhexosaminidase from Aspergillus oryzae, achieving yields of up to 57%. Subsequently, enzymatic deacetylation of chitooligomers with DP 6 and 7 was accomplished using peptidoglycan deacetylase from Bacillus subtilis BsPdaC. The innovative enzymatic procedure demonstrates a sustainable and feasible route for converting waste chitin into unavailable bioactive chitooligomers potentially applicable as natural pesticides in ecological and sustainable agriculture.

Identifying Chlorella vulgaris and Chlorella sorokiniana as sustainable organisms to bioconvert glucosamine into valuable biomass

Chitin is a major component of various wastes such as crustacean shells, filamentous fungi, and insects. Recently, food-safe biological and chemical processes converting chitin to glucosamine have been developed. Here, we studied microalgae that can uptake glucosamine as vital carbon and nitrogen sources for valuable alternative protein biomass. Utilizing data mining and bioinformatics analysis, we identified 29 species that contain the required enzymes for glucosamine to glucose conversion. The growth performance of the selected strains was examined, and glucosamine was used in different forms and concentrations. Glucose at a concentration of 2.5 g/L was required to initiate glucosamine metabolic degradation by Chlorella vulgaris and Chlorella sorokiniana. Glucosamine HCl and glucosamine phosphate showed maximum cell counts of about 8.5 and 9.0 log/mL for C. sorokiniana and C. vulgaris in 14 days, respectively. Enzymatic hydrolysis of glucosamine increased growth performance with C. sorokiniana by about 3 folds. The adapted strains were fast-growing and could double their dry biomasses during the same incubation time. In addition, adapted C. sorokiniana was able to tolerate three times glucosamine concentration in the medium. The study illustrated possible strategies for employing C. sorokiniana and C. vulgaris to convert glucosamine into valuable biomass in a more sustainable way.

Aspergillus niger fermentation residues application to produce biochar for the anode of lithium-ion batteries

Aspergillus niger is widely applied in the fermentation industry, but produce abundant mycelium residues every year. As a kind of solid waste, mycelium residues seriously affect the environment. How to manage and utilize this solid waste is a problem for the fermentation industry. It was reported that many kinds of biomass could be utilized to produce carbon materials, which would be further used to produce lithium-ion rechargeable batteries (LIBs). Here, porous biochar was prepared from A. niger mycelial residues and further used as an anode for LIBs. Since the A. niger mycelium contains abundant nitrogen (5.29%) from its chitosan-dominated cell wall, and silicon (9.63%) from perlite filter aid, respectively, the biochar presented an excellent cycle stability and rate performance when applied as the anode of LIBs. The conclusion of this research shows the wide application prospect of fungal fermentation residues as carbon precursors in energy storage devices. Meanwhile, this investigation provides an alternative management method for A. niger mycelium residues, with which the mycelium residues could be effectively recycled to avoid resource waste and environmental pollution.

An overview of fungal chitinases and their potential applications

Chitin, the world's second most abundant biopolymer after cellulose, is composed of β-1,4-N-acetylglucosamine (GlcNAc) residues. It is the key structural component of many organisms, including crustaceans, mollusks, marine invertebrates, algae, fungi, insects, and nematodes. There has been a significant increase in the generation of chitinous waste from seafood businesses, resulting in a big amount of scrap. Although several organisms, such as plants, crustaceans, insects, nematodes, and animals, produce chitinases, microorganisms are promising candidates and a sustainable option that mediates chitin degradation. Fungi are the dominant group of chitinase producers among microorganisms. In fungi, chitinases are involved in morphogenesis, cell division, autolysis, chitin acquisition for nutritional purposes, and mycoparasitism. Many efficient chitinolytic fungi with potential applications have been identified in a variety of environments, including soil, water, marine wastes, and plants. The current review highlights the key sources of chitinolytic fungi and the characterization of fungal chitinases. It also discusses the applications of fungal chitinases and the cloning of fungal chitinase genes.

Biochemical Properties of a Cold-Active Chitinase from Marine Trichoderma gamsii R1 and Its Application to Preparation of Chitin Oligosaccharides

The enzymatic degradation of different chitin polymers into chitin oligosaccharides (COSs) is of great significance given their better solubility and various biological applications. Chitinase plays a pivotal role in the enzymatic preparation of COSs. Herein, a cold-adapted and efficient chitinase (ChiTg) from the marine Trichoderma gamsii R1 was purified and characterized. The optimal temperature of ChiTg was 40 °C, and the relative activity at 5 °C was above 40.1%. Meanwhile, ChiTg was active and stable from pH 4.0 to 7.0. As an endo-type chitinase, ChiTg exhibited the highest activity with colloidal chitin, then with ball-milled and powdery chitin. In addition, ChiTg showed high efficiency when hydrolyzing colloidal chitin at different temperatures, and the end products were mainly composed of COSs with one to three degrees of polymerization. Furthermore, the results of bioinformatics analysis revealed that ChiTg belongs to the GH18 family, and its acidic surface and the flexible structure of its catalytic site may contribute to its high activity in cold conditions. The results of this study provide a cold-active and efficient chitinase and ideas for its application regarding the preparation of COSs from colloidal chitin.

Simultaneous Production of Cellulase and β-Carotene in the Filamentous Fungus Trichoderma reesei

β-Carotene is an indispensable additive in beverage, cosmetic, feed, and pharmaceutical production. The fermentation industry annually generates abundant waste mycelia from Trichoderma reesei (T. reesei), a pivotal industrial strain for cellulase and heterologous protein production. In this study, we constructed a T. reesei cell factory for β-carotene production for the first time. Four key enzymes, CarRP, CarB, GGS1/CrtE, and HMG1, were overexpressed in T. reesei. The concentrations of medium components, including tryptone and glucose, were optimized. The modified strain accumulated β-carotene at a titer of 218.8 mg/L in flask culture. We achieved cellulase production (FPase, 22.33 IU/mL) with the concomitant production of β-carotene (286.63 mg/L) from T. reesei in a jar. Overall, this study offers a novel and unique approach to address the costly waste mycelium management process using T. reesei industrial strains that simultaneously produce proteins and carotenoids.

Purification and characterization of a chitinase from Aeromonas media CZW001 as a biocatalyst for producing chitinpentaose and chitinhexaose

Developing chitinase suitable for the bioconversion of chitin to chitin oligosaccharides has attracted significant attention due to its benefits in environmental protection. In this study, chitinase from Aeromonas media CZW001 (AmChi) was purified and characterized. The molecular weight of AmChi was approximately 40 kDa. AmChi exhibited maximum catalytic activity at pH 8.0 with an optimum temperature of 55°C and showed broad stability between 15 and 65°C and between pH 5.0 and 9.0. AmChi was activated by Mg²⁺ , Na⁺ , and K⁺ and inhibited by Hg⁺ , Co²⁺ , Fe²⁺ , Ca²⁺ , Ag⁺ , Zn²⁺ , and EDTA. The main products of AmChi on colloidal chitin were chitinhexaose and chitinpentaose. AmChi had better substrate specificity for powdered chitin than colloidal chitin and had a higher catalytic efficiency toward (GlcNAc)₅ than colloidal chitin. AmChi inhibited fungal growth in a dose-dependent manner. These results suggest that AmChi could be used for the enzymatic degradation of chitin to produce chitinhexaose and chitinpentaose, which have several industrial applications.

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.

Lynamicin B is a Potential Pesticide by Acting as a Lepidoptera-Exclusive Chitinase Inhibitor

Insect group h chitinase is a promising target for designing non-target safe pesticides in that it is exclusively distributed in lepidopteran insects, over 80% of which are agricultural pests. In this work, lynamicin B was discovered to be an inhibitor of OfChi-h, the group h chitinase from the lepidopteran pest Ostrinia furnacalis. Lynamicin B was revealed to competitively inhibit OfChi-h with a K_i value of 8.76 μM and does not significantly inhibit other chitinases. The co-crystal structure of lynamicin B and OfChi-h revealed that the dichloroindolyl group of lynamicin B occupies an unexplored pocket below subsites +1 and +2 of the substrate-binding cleft, which is vital for its selectivity. Feeding experiments demonstrated that lynamicin B exhibited high insecticidal activities against other lepidopteran pests Mythimna separata and Spodoptera frugiperda besides O. furnacalis. Moreover, lynamicin B did not affect Trichogramma ostriniae, a natural enemy of O. furnacalis. This study provides a natural-derived potent pesticide for the control of lepidopteran pests, leaving its natural enemy unaffected.