Degradation of Chitin and Chitosan by a Recombinant Chitinase Derived from a Virulent Aeromonas hydrophila Isolated from Diseased Channel Catfish

Abstract

A chitinase was identified in extracellular products of a virulent Aeromonas hydrophila isolated from diseased channel catfish (Ictalurus punctatus). Recombinant chitinase (rChi-Ah) was produced in Escherichia coli. Purified rChi-Ah had optimal activity at temperature of 42˚C and pH 6.5. The affinity (Km) for chitosan was 4.18 mg•ml −1 with Vmax of 202.5 mg•min −1 •mg −1. With colloidal chitin as substrate, rChi-Ah generated N,N'-diacetyl-glucosamine predominantly. Conversion of chitosan (≥75% deacetylated) by rChi-Ah revealed five major products: 2 to 4 units of glucosamine, all of which had at least one acetyl group. It was determined that N-acetylated glucosamine was the recognition and cleavage site of rChi-Ah; the minimal and maximal cleavages were two and four glucosamine units, respectively. Functional analysis of rChi-Ah suggests that A. hydrophilachi-tinase is a bioactive chitinolytic enzyme, which may benefit the pathogen for survival and/or infection .