IN-VITRO ACTIVITY OF THE LIMULUS ANTIMICROBIAL PEPTIDE TACHYPLESIN-I ON MARINE BIVALVE PATHOGENS

Tachyplesin 1 is an antimicrobial peptide extracted from hemocytes of the Japanese horseshoe crab Tachypleus tridentatus. We studied the in vitro activity of tachyplesin I against bivalve pathogens: the oyster parasites Bonamia ostreae, the intrahemocytic parasite of the flat oys ter Ostrea edulis and Perkinsus marinus, the histozoic parasite of the Eastern oyster Crassostrea virginica, and the bacterium Vibrio P1, pa thogenic for the clam Tapes philippinarum. Viability of the protozoans was assessed microscopically by the uptake of the vital dyes acridine orange and ethidium bromide. Following exposure to tachyplesin I, B. ostreae and P. marinus viabilities were reduced in a dose-dependent ma nner, up to, respectively, 94 and 62% within a 500 mu g/ml peptide con centration. The fine structure of P. marinus was highly altered by the peptide, Tachyplesin I also displayed a potent activity against marin e vibrios, with a MIC of 0.4-0.8 mu g/ml against Vibrio PI. We examine d the morphology of oyster hemocytes treated by tachyplesin I, togethe r with the cell functional capabilities to produce chemiluminescence. No effect of the peptide was found on bivalve host cells. As transgeni c technology is currently being applied to marine invertebrates, these results indicate that tachyplesin I may provide effective gene sequen ces to be manipulated in order to produce disease-resistant bivalves.