Expression and characterization of two chitinases with synergistic effect and antifungal activity from Xenorhabdus nematophila

Functional Comparison of Three Chitinases from Symbiotic Bacteria of Entomopathogenic Nematodes

Xenorhabdus and Photorhabdus, bacterial symbionts of entomopathogenic nematodes Steinernema and Heterorhabditis, respectively, have several biological activities including insecticidal and antimicrobial activities. Thus, XnChi, XhChi, and PtChi, chitinases of X. nematophila, X. hominickii, and P. temperata isolated from Korean indigenous EPNs S. carpocapsae GJ1-2, S. monticolum GJ11-1, and H. megidis GJ1-2 were cloned and expressed in Escherichia coli BL21 to compare their biological activities. Chitinase proteins of these bacterial symbionts purified using the Ni-NTA system showed different chitobiosidase and endochitinase activities, but N-acetylglucosamidinase activities were not shown in the measuring of chitinolytic activity through N-acetyl-D-glucosarmine oligomers. In addition, the proteins showed different insecticidal and antifungal activities. XnChi showed the highest insecticidal activity against Galleria mellonella, followed by PtChi and XhChi. In antifungal activity, XhChi showed the highest half-maximal inhibitory concentration (IC50) against Fusarium oxysporum with 0.031 mg/mL, followed by PtChi with 0.046 mg/mL, and XnChi with 0.072 mg/mL. XhChi also showed the highest IC50 against F. graminearum with 0.040 mg/mL, but XnChi was more toxic than PtChi with 0.055 mg/mL and 0.133 mg/mL, respectively. This study provides an innovative approach to the biological control of insect pests and fungal diseases of plants with the biological activity of symbiotic bacterial chitinases of entomopathogenic nematodes.

Insecticidal Activity of Chitinases from Xenorhabdus nematophila HB310 and Its Relationship with the Toxin Complex

Xenorhabdus nematophila HB310 secreted the insecticidal protein toxin complex (Tc). The chi60 and chi70 chitinase genes are located on the gene cluster encoding Tc toxins. To clarify the insecticidal activity of chitinases and their relationship with Tc toxins, the insecticidal activity of the chitinases was assessed on Helicoverpa armigera. Then, the chi60 and chi70 genes of X. nematophila HB310 were knocked out by the pJQ200SK suicide plasmid knockout system. The insecticidal activity of Tc toxin from the wild-type strain (WT) and mutant strains was carried out. The results demonstrate that Chi60 and Chi70 had an obvious growth inhibition effect against the second instar larvae of H. armigera with growth-inhibiting rates of 81.99% and 90.51%, respectively. Chi70 had a synergistic effect with the insecticidal toxicity of Tc toxins, but Chi60 had no synergistic effect with Tc toxins. After feeding Chi60 and Chi70, the peritrophic membrane of H. armigera became inelastic, was easily broken and leaked blue dextran. The Δchi60, Δchi70 and Δchi60-chi70 mutant strains were successfully screened. The toxicity of Tc toxins from the WT, Δchi60, Δchi70 and Δchi60-chi70 was 196.11 μg/mL, 757.25 μg/mL, 885.74 μg/mL and 20,049.83 μg/mL, respectively. The insecticidal activity of Tc toxins from Δchi60 and Δchi70 was 3.861 and 4.517 times lower than that of Tc toxins from the WT, respectively, while the insecticidal activity of Tc toxins from the Δchi60-chi70 mutant strain almost disappeared. These results indicate that the presence of chi60 and chi70 is indispensable for the toxicity of Tc toxins.

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.

Microbial chitinases: properties, enhancement and potential applications

Chitinases are a category of hydrolytic enzymes that catalyze chitin and are formed by a wide variety of microorganisms. In nature, microbial chitinases are primarily responsible for chitin decomposition and play a vital role in the balance of carbon and nitrogen ratio in the ecosystem. The physicochemical attributes and the source of chitinase are the main bases that determine their functional characteristics and hydrolyzed products. Several chitinases have been reported and characterized, and they obtain a wider consideration for their utilization in a large number of uses such as in agriculture, food, environment, medicine and pharmaceutical companies. The antifungal and insecticidal impacts of several chitinases have been extensively studied, aiming to protect crops from phytopathogenic fungi and insects. Chitooligosaccharides synthesized by chitin degradation have been shown to improve human health through their antimicrobial, antioxidant, anti-inflammatory and antitumor properties. This review aims at investigating chitinase production, properties and their potential applications in various biotechnological fields.

Microbial chitinases: properties, current state and biotechnological applications

Chitinases are a group of hydrolytic enzymes that catalyze chitin, nd are synthesized by a wide variety of organisms. In nature, microbial chitinases are primarily responsible for chitin decomposition. Several chitinases have been reported and characterized, and they are garnering increasing attention for their uses in a wide range of applications. In the food industry, the direct fermentation of seafood, such as crab and shrimp shells, using chitinolytic microorganisms has contributed to increased nutritional benefits through the enhancement of chitin degradation into chitooligosaccharides. These compounds have been demonstrated to improve human health through their antitumor, antimicrobial, immunomodulatory, antioxidant, and anti-inflammatory properties. Moreover, chitinase and chitinous materials are used in the food industry for other purposes, such as the production of single-cell proteins, chitooligosaccharides, N-acetyl D-glucosamines, biocontrol, functional foods, and various medicines. The functional properties and hydrolyzed products of chitinase, however, depend upon its source and physicochemical characteristics. The present review strives to clarify these perspectives and critically discusses the advances and limitations of microbial chitinase in the further production of functional foods.