Purification and characterization of an antibacterial substance produced by a marine Alteromonas species

An extracellular inhibitory substance produced by the marine Alteromonas strain P-31 (NCMB 2144) was isolated and purified. The inhibitor was a macromolecule with a molecular weight of 90,000 estimated by Sephadex G-100 chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The inhibitory activity was antagonized by proteinase K and beta-amylase and inactivated by heating at 80 degrees C for 30 min. The purified substance exhibited two typical absorption bands in the infrared spectrum at 1,650 and 1,075 cm-1, corresponding to peptide linkages and carbohydrate residues, respectively. These findings allowed us to characterize the antimicrobial compound as a thermolabile glycoprotein. The substance exhibited a broad inhibitory spectrum, being active against clinical and environmental isolates from related and nonrelated taxonomical bacterial groups as well as against the producer strain and other similar marine bacterial strains. The inhibitory glycoprotein did not display cytotoxicity toward mammalian and fish cell lines.