Submitted to: Advances in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/9/2015
Publication Date: 8/26/2015
Publication URL: http://handle.nal.usda.gov/10113/62196
Citation: Zhang, D., Bland, J.M., Xu, D., Chung, S. 2015. Degradation of chitin and chitosan by a recombinant chitinase derived from a virulent Aeromonas hydrophila isolated from diseased channel catfish. Advances in Microbiology. 5:611-619.
Interpretive Summary: A chitinase was identified in extracellular products of a virulent Aeromonas hydrophila, the important pathogen of channel catfish. To understand the role of the chitinase in A. hydrophila, the chitinase-encoding gene was cloned from the bacterium’s genomic DNA and heterologously produced in Escherichia coli. Recombinant chitinase (rChi-Ah) produced in E. coli was biochemically characterized in this study. Using colloidal chitin and chitosan (partially de-acetylated chitin) as substrates, rChi-Ah actively converted the chitin into N,N’-diacetyl-glucosamine and the chitosan into 2 to 4 units of glucosamine. Since N,N’-diacetyl-glucosamine was reported to be an inhibitor of mammal lysozyme C and lysozyme C in fish was an innate immune defense protein, it is postulated that A. hydrophila may benefit from the chitinolytic products for survival and/or infection. The degradation products of chitin by rChi-Ah are therefore of interest in studying interaction between A. hydrophila and fish.
Technical Abstract: A chitinase was identified in extracellular products of a virulent Aeromonas hydrophila isolated from diseased channel catfish (Ictalurus punctatus). Bioactive 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 162 mg min-1 mg-1. With home-made colloidal chitin as substrate, rChi-Ah generated N,N’-diacetyl-glucosamine predominantly. Conversion of chitosan (equal to or greater than 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 is postulated that N-acetylated glucosamine is the recognition and cleavage site of rChi-Ah; the minimal and maximal cleavages are two and four glucosamine units, respectively. Whether A. hydrophila benefits from the chitinolytic products for survival and/or infection merits further investigation. Additionally, since chitooligosaccharides have many interesting bioactivities, rChi-Ah is a useful chitinolytic enzyme for extensive research in related fields.