Isolation and Identification of a Novel Inducible Antibacterial Peptide from the Skin Mucus of Japanese Eel, Anguilla japonica

In this study, acetone extracts and acidic extracts were prepared from skin mucus, gill, kidney, liver and spleen of the Japanese eel, Anguilla japonica, and they exhibited different levels of antibacterial activities against three strains of Gram-negative bacteria, Edwardsiella tarda, Aeromonas hydrophila, Aeromonas sp. and one Gram-positive bacterium Micrococcus leteus. The mucus was chosen as the source of antibacterial peptide for further purification of antibacterial peptides. Following the intraperitoneal injection of A. hydrophila, one of the main pathogenic bacteria of Japanese eel and many other fish, a peptide was purified from acetic acid extraction of the skin mucus, by using cationic exchange liquid chromatography and reverse-phase high-performance liquid chromatography (RP-HPLC). The isolated antibacterial peptide, named as AJN-10, exhibited antibacterial activity against A. hydrophila. The AJN-10 is a heat-tolerant and hydrophilic peptide. The molecular weight of this peptide is 6,044.28 Da, as determined by matrix-assisted laser desorption ionisation time of flight mass spectrometry. The 20 N-terminal amino acid sequences were clarified by Edman degradation, and based on results of homology search by BLAST analysis of the 20 N-terminal sequences, the AJN-10 showed little similarity to other proteins in databases