Characterization of an Atypical GH19 Family Chitinase from Vibrio jasicida KMM 6832

The highly chitinolytic marine bacterium <i>Vibrio jasicida</i> KMM 6832, which exhibits potent antifungal activity, possesses an atypical Glycosyl Hydrolase family 19 (GH19) chitinase (ChitVjs). This is the first report of a GH19 gene in <i>V. jasicida</i>, an enzyme generally absent in this species and rare within the Harveyi clade. Phylogenetically, ChitVjs-like enzymes from the genera <i>Vibrio</i> and <i>Aeromonas</i> form a distinct cluster, separate from typical plant and bacterial GH19 counterparts. Despite high sequence identity (80-94%) with characterized homologs from <i>V. parahaemolyticus</i> and <i>V. cholerae</i>, ChitVjs is distinguished by its obligate halophilicity (optimum 0.3-0.4 M NaCl), an acidic isoelectric point (pI 4.72), and a broader cation-activation profile (K⁺, Ni²⁺, Ca²⁺, Cu²⁺, Co²⁺). The recombinant ChitVjs was produced in <i>E. coli</i> as a soluble 63 kDa protein. It functions as a stable, salt-dependent endo-chitinase/chitosanase, exhibiting optimal activity at 40 °C and pH 7.0. The enzyme displays high affinity for colloidal chitin (<i>K_M</i> 0.377 mg·mL^-1), is activated by DTT and Tween 80, and shows moderate stability in organic solvents. Furthermore, unlike its primarily catabolic relatives, ChitVjs suppresses conidial germination in marine-derived <i>Aspergillus</i> strains. These findings suggest that ChitVjs significantly contributes to the competitive fitness of <i>V. jasicida</i> KMM 6832 in high-salinity marine environments through both nutrient acquisition and antagonism.