Mining a vibriophage depolymerase for enhanced pathogen control in aquaculture

ABSTRACT Despite the promise of phages as antibiotic alternatives, their efficacy is often undermined by the rapid emergence of bacterial resistance. Phage-derived enzymes, particularly depolymerases, offer a compelling strategy to overcome this limitation and enhance antibacterial therapy. Focusing on Vibrio pathogens, the major threats to global aquaculture, our bioinformatic analysis revealed that 79.4% of cultured and 46.2% of uncultured Vibrio phages encode putative depolymerases, underscoring a vast but underexploited antibacterial resource. We further isolated and characterized VnaP, a depolymerase-encoding phage (novel genus, Caudovircetes ) that forms distinctive halo plaques indicative of depolymerase activity. Genome analysis identified ORF193, encoding a novel polysaccharide depolymerase lacking sequence or structural homology to any characterized depolymerases. Heterologously expressed Dep193 efficiently degraded Vibrio surface polysaccharides and exhibited potent antibiofilm activity. While Dep193 exhibits modest standalone antibacterial activity, its synergistic combination with VnaP significantly enhances bacterial clearance and delays resistance emergence across multiple Vibrio species. As the first biochemically validated Vibrio phage depolymerase, Dep193 broadens the known diversity of these enzymes and establishes an effective strategy for Vibrio control in aquaculture. IMPORTANCE The rapid emergence of antibiotic-resistant Vibrio strains threatens global aquaculture sustainability, necessitating alternative antimicrobial strategies. This study identifies and characterizes Dep193, a novel phage-encoded depolymerase with polysaccharide-degrading and antibiofilm activities that enhances phage therapy efficacy through a previously unreported mechanism. The Dep193-phage VnaP combination exhibits broad-spectrum activity against multiple Vibrio species, demonstrating strong potential as a therapeutic strategy for aquaculture. Notably, Dep193 lacks any recognizable functional domains found in characterized depolymerases, representing the first validated member of a novel evolutionary clade. These findings expand the known diversity of phage depolymerases and provide a promising avenue for the targeted control of Vibrio infections in aquaculture.