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Degradation of chitin and chitosan by a recombinant chitinase derived from a virulent Aeromonas hydrophila isolated from diseased channel catfish

Dunhua Zhang, John M. Bland, Dehai Xu, Siyin Chung
Advances in microbiology 2015 v.5 no.9 pp. 611-619
Aeromonas hydrophila, Escherichia coli, Ictalurus punctatus, chitin, chitinase, chitosan, glucosamine, microbiology, pH, pathogen survival, recombinant proteins, temperature, virulence
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. hydrophilachitinase is a bioactive chitinolytic enzyme, which may benefit the pathogen for survival and/or infection.