Identification of an endo-chitinase from Corallococcus sp. EGB and evaluation of its antifungal properties

As the main component of the fungal cell wall, chitin has been regarded as an optimal molecular target for the biocontrol of plant-pathogenic fungi. In this study, the chitin hydrolase CcCti1, which belongs to the glycoside hydrolase family 18 (GH 18) and exhibits potential antifungal activity, was identified from Corallococcus sp. EGB. CcCti1 lacks a fibronectin type-III (FN3) domain that is present in similar enzymes from most genera of myxobacteria, indicating that CcCti1 may have acquired chitinase activity due to the FN3 domain deletion during myxobacterial evolution. CcCti1 was expressed in Escherichia coli BL21 (DE3) with a specific activity of up to 10.5 U/μmol with colloidal chitin as the substrate. Product analysis showed that CcCti1 could hydrolyze chitin into N-acetylated chitohexaose (GlcNAc)₆ as the major product, in addition to chitooligosaccharides. The analysis of biochemical properties indicated that the CBD and FN3 domains in CcCti1 determine the substrate affinity and pH stability. Otherwise, CcCti1 exhibited efficient biocontrol activity against the plant pathogen Magnaporthe oryzae in a dose-dependent manner, inhibiting the conidia germination and appressoria formation at a concentration of 0.08 mg/mL. Overall, the chitohexaose-producing chitinase CcCti1 with hydrolytic features may find potential application in chitin conversion and biocontrol of fungal plant diseases.