Preparation of chitooligosaccharides with a low degree of polymerization and anti-microbial properties using the novel chitosanase AqCsn1

Chitosanases hydrolyze chitosan into chitooligosaccharides (COSs) with various biological activities, which are widely employed in many areas including plant disease management. In this study, the novel chitosanase Aq Csn1 belonging to the glycoside hydrolase family 46 (GH46) was cloned from Aquabacterium sp. A7-Y and heterologously expressed in Escherichia coli BL21 (DE3). Aq Csn1 displayed the highest hydrolytic activity towards chitosan with 95% degree of deacetylation at 40 °C and pH 5.0, with a specific activity of 13.18 U/mg. Product analysis showed that Aq Csn1 hydrolyzed chitosan into (GlcN) 2 and (GlcN) 3 as the main products, demonstrating an endo-type cleavage pattern. Evaluation of antagonistic activity showed that the hydrolysis products of Aq Csn1 suppress the mycelial growth of Magnaporthe oryzae and Phytophthora sojae in a concentration-dependent manner, and the inhibition rate of P. sojae reached 39.82% at a concentration of 8 g/L. Our study demonstrates that Aq Csn1 and hydrolysis products with a low degree of polymerization might have potential applications in the biological control of agricultural diseases.