Bioactive Peptides from Epibiotic Pseudoalteromonas Strain P1

Abstract

An epibiotic bacterial strain designated as P1 with characteristic colony morphology was isolated from five random samplings of the sea fan coral Junceella juncea (Pallas, 1766). Phylogenetic identification based on comparative sequence analysis of 16Ss rRNA gene indicated that the stain P1 fell under the genera Pseudoalteromonas. In the initial screening using agar overlay method the Pseudoalteromonas strain P1 was found to exhibit broad spectral activity inhibiting 7 out of 10 test strains. A highest zone of 25mm was noted against two bacterial strains, B. subtilis and S. typhi. The strain P1 formed a distinct biofilm layer over the marine broth (air-liquid interface) in static culture at room temperature. The active component was also found to be adsorbed on the biofilm layer. Protease digestion of the crude extract resulted in the loss of activity indicating the protenacious nature of the active molecules. Bioassay guided purification using anion exchange chromatography and RP-HPLC yielded a molecule with antimicrobial activity. Mass spectrophotometry analysis has shown that this molecule has a mass of 1115Da. In cation exchange purification, two molecules of masses 1520 and 1542Da were found in the active fraction. Morphological and physiological characterization of the Pseudolateromonas strain P1 shown it to be a pigmented, motile, catalase and oxidase positive rod. Studies regarding epibotic bacteria in Indian waters have been few. This study highlights the importance of epibiotic bacteria associated with corals as a potential source for the discovery of novel antimicrobial and other natural products.