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

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℃?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.

Peanut Allergens Attached with p-Aminobenzamidine Are More Resistant to Digestion than Native Allergens

Despite being known as resistant proteins, peanut allergens (Ara h 1 and Ara h 2) can be digested and cause allergic reactions. Making the allergens more resistant to digestion may aid in non-absorption and excretion of the allergens. Our objectives were to make Ara h 1 and Ara h 2 more resistant to digestion and test them in a model system using trypsin as the digestive enzyme. The resistant allergens were prepared by covalently attaching p-aminobenzamidine (pABA), a protease inhibitor, to peanut allergens in an extract or on a PVDF membrane using glutaraldehyde, and were then tested for resistance to trypsin digestion. SDS-PAGE and Western blot were performed to determine the allergenic capacity of the modified allergens. A control was prepared using glycine instead. Results showed that Ara h 2, when covalently attached with pABA, was more resistant to trypin digestion than the native allergen. Similarly, Ara h 1, prepared on a PVDF membrane and treated with pABA, displayed a resistance to trypsin digestion. Treatment of the allergens with glycine (a control) instead of pABA showed that the modified allergens were as digestible as native allergens. Blot assays showed that the pABA-treated allergens exhibited a lower allergenic capacity than native allergens. It was concluded that pABA, when attached to peanut allergen Ara h 1 or Ara h 2, inhibited digestion of the allergen by trypsin and reduced their allergenic capacity as well.

Edwardsiella tarda and Aeromonas hydrophila isolated from diseased Southern flounder(Paralichthys lethostigma)are virulent to channel catfish and Nile tilapia

Objective:To identify bacteria isolated from diseased Southern flounder and determine whether they are virulent to channel catfish and Nile tilapia.Methods:Gram-negative bacteria isolates were recovered from five tissues of diseased Southern flounder(Paralichthys lethostigma).The isolates were subjected to biochemical and molecular identification followed by virulence study in fish.Results:Based on biochemical analysis,the 25 isolates were found to share homologies with either Edwardsiella tarda(E.tarda)or Aeromonas hydrophila(A.hydrophila).Based on sequencing results of partial 16S rRNA gene,15 isolates shared 100%identities with the 16S rRNA sequence of previously identified E.tarda strain TX1,whereas the other 10 isolates shared 100%identities with the 16S rRNA sequence of previously identified A.hydrophila strain An4.When healthy fish were exposed to flounder isolate by intracoelomic injection,the LD50 values of flounder isolate E.tarda to channel catfish or Nile tilapia[(10±2)g]were 6.1×10^(4)and 1.1×10^(7)CFU/fish,respectively,whereas that of flounder isolate A.hydrophila to channel catfish and Nile tilapia were 1.4×10^(7)and 5.6×10^(7)CFU/fish,respectively.Conclusions:This is the first report that E.tarda and A.hydrophila isolated from diseased Southern flounder are virulent to catfish and tilapia.