Biochemical Properties of a Novel Cold-Adapted GH19 Chitinase with Three Chitin-Binding Domains from Chitinilyticum aquatile CSC-1 and Its Potential in Biocontrol of Plant Pathogenic Fungi.

GH19 (glycoside hydrolase 19) chitinases play crucial roles in the enzymatic conversion of chitin and biocontrol of phytopathogenic fungi. Herein, a novel multifunctional chitinase of GH19 ( Ca Chi19A), which contains three chitin-binding domains (ChBDs), was successfully cloned from Chitinilyticum aquatile CSC-1 and heterologously expressed in Escherichia coli . We also generated truncated mutants of Ca Chi19A_ΔI, Ca Chi19A_ΔIΔII, and Ca Chi19A_CatD consisting of two ChBDs and a catalytic domain, one ChBD and a catalytic domain, and only a catalytic domain, respectively. Ca Chi19A, Ca Chi19A_ΔI, Ca Chi19A_ΔIΔII, and Ca Chi19A_CatD exhibited cold adaptation, as their relative enzyme activities at 5 °C were 40.7, 51.6, 66.2, and 82.6%, respectively. Compared with Ca Chi19A and other variants, Ca Chi19A_ΔIΔII demonstrated a higher level of stability below 50 °C and retained relatively high activity over a wide pH range of 5-12. Analysis of the hydrolysis products revealed that Ca Chi19A and Ca Chi19A_ΔIΔII exhibit exoacting, endoacting, and N -acetyl-β-d-glucosaminidase activities toward colloidal chitin. Furthermore, Ca Chi19A and Ca Chi19A_ΔIΔII exhibited inhibitory effects on the hyphal growth of Fusarium oxysporum , Fusarium redolens , Fusarium fujikuroi , Fusarium solani, and Coniothyrium diplodiella , thereby illustrating effective biocontrol activity. These results indicated that Ca Chi19A and Ca Chi19A_ΔIΔII show advantages in some applications where low temperatures were demanded in industries as well as the biocontrol of fungal diseases in agriculture.