Enzymatic Properties of Chitosanase from Bacillus velezensis YB1534 and Antibacterial Activity of Its Oligosaccharide Products

Chitosan oligosaccharides (COSs), obtained through the hydrolysis of chitosan, exhibit remarkable antibacterial properties. In pursuit of COSs with enhanced antibacterial activity, the enzymatic characteristics of the chitosanase from <i>Bacillus velezensis</i> YB1534 (BvChi) were investigated. The purified BvChi displayed optimal activity at pH 6.0 and 50 °C and showed the highest hydrolytic activity using colloidal chitosan as a substrate, with the presence of Mn²⁺. The COSs produced by enzymatic hydrolysis of BvChi exhibited a minimum degree of polymerization (DP) of 2, and their antimicrobial activities against certain pathogenic bacteria (<i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, <i>Salmonella typhi</i> 50071, and <i>Aeromonas hydrophila</i>) were evaluated. Among them, the 20 min hydrolysate showed the strongest growth inhibition against all these pathogens, demonstrated by the inhibition zone diameters, and its MIC and MBC values toward <i>A. hydrophila</i> were 0.625 and 1.25 mg/mL, respectively. Thin-layer chromatography (TLC) analysis showed that the hydrolyzed products after 20 min contains more COSs with DP > 5. These findings highlighted the potential of BvChi as a biocatalyst for producing antimicrobial COSs, applicable in food preservation and biomedical fields.