Host-derived antimicrobial peptides enhance survival in Vibrio-infected scallop larvae through dual antibacterial and immunomodulatory actions.

Scallop aquaculture is increasingly threatened by larval mortality caused by Vibrio bacteria, highlighting the need for sustainable pathogen control strategies. In a previous study, we designed and synthesized two novel cationic antimicrobial peptides (AMPs) derived from Argopecten purpuratus, a key scallop species in Chilean and Peruvian aquaculture, namely Helixidin and N-ter ApBD Q13R. These AMPs exhibited strong antibacterial activity and distinct mechanisms of action against host-associated vibrio strains while being innocuous to scallop larvae. In the present study, we evaluated the therapeutic potential of these synthetic AMPs, administered individually and in combination, in A. purpuratus veliger and pediveliger larvae experimentally infected with the pathogenic strain Vibrio bivalvicida VPAP30, and explored the potential mechanisms underlying their protective effects. Our results demonstrated that (i) Helixidin and N-ter ApBD Q13R significantly increased larval survival following VPAP30 infection; (ii) this protective effect is partly explained by their direct inhibition of VPAP30 growth; (iii) the combination of both AMPs upregulates immune-related genes associated with the TLR-IκB-BD pathway in uninfected pediveliger larvae, suggesting a potential immune-priming effect; and (iv) in silico analyses revealed potential molecular interactions between the AMPs and Gram-negative bacterial membranes, as well as with the pattern recognition receptor ApTLR. These findings suggest that Helixidin and N-ter ApBD Q13R represent a promising and sustainable strategy for managing Vibrio infections in scallop aquaculture, aligning with broader goals of maintaining healthy marine ecosystems and supporting industry sustainability.