In VitroActivity of the Limulus Antimicrobial Peptide Tachyplesin I on Marine Bivalve Pathogens

Abstract

Tachyplesin 1 is an antimicrobial peptide extracted from hemocytes of the Japanese horseshoe crabTachypleus tridentatus. We studied thein vitroactivity of tachyplesin I against bivalve pathogens: the oyster parasitesBonamia ostreae,the intrahemocytic parasite of the flat oysterOstrea edulisandPerkinsus marinus,the histozoic parasite of the Eastern oysterCrassostrea virginica,and the bacteriumVibrioP1, pathogenic for the clamTapes 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. ostreaeandP. marinusviabilities were reduced in a dose-dependent manner, up to, respectively, 94 and 62% within a 500 μg/ml peptide concentration. The fine structure ofP. marinuswas highly altered by the peptide. Tachyplesin I also displayed a potent activity against marine vibrios, with a MIC of 0.4–0.8 μg/ml againstVibrioP1. We examined the morphology of oyster hemocytes treated by tachyplesin I, together with the cell functional capabilities to produce chemiluminescence. No effect of the peptide was found on bivalve host cells. As transgenic technology is currently being applied to marine invertebrates, these results indicate that tachyplesin I may provide effective gene sequences to be manipulated in order to produce disease-resistant bivalves.