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

TL;DR

This paper describes a unique chitinase enzyme from a marine bacterium that helps it thrive in salty environments by breaking down chitin and fighting fungi.

Contribution

The first characterization of an atypical GH19 chitinase in Vibrio jasicida with distinct biochemical and functional properties.

Findings

ChitVjs is a halophilic endo-chitinase with optimal activity at 40 °C and pH 7.0.

The enzyme suppresses fungal spore germination and is activated by multiple cations.

ChitVjs has high affinity for colloidal chitin and is stable in organic solvents.

Abstract

The highly chitinolytic marine bacterium Vibrio jasicida 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 V. jasicida, an enzyme generally absent in this species and rare within the Harveyi clade. Phylogenetically, ChitVjs-like enzymes from the genera Vibrio and Aeromonas form a distinct cluster, separate from typical plant and bacterial GH19 counterparts. Despite high sequence identity (80–94%) with characterized homologs from V. parahaemolyticus and V. cholerae, 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 E. coli 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 (KM 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 Aspergillus strains. These findings suggest that ChitVjs significantly contributes to the competitive fitness of V. jasicida KMM 6832 in high-salinity marine environments through both nutrient acquisition and antagonism.

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