Role of the Vibriolysin VemA Secreted by the Emergent Pathogen Vibrio europaeus in the Colonization of Manila Clam Mucus

Vibrio europaeus is an emergent pathogen affecting clams, oysters and scallops produced in the most important countries for bivalve aquaculture. Studies concerning virulence factors involved in the virulence of V. europaeus are very scarce despite its global significance for aquaculture. Zinc-metalloproteases have been described as a major virulence factor in some Vibrio spp., although their contribution and role in the virulence of V. europaeus is not clear. To address this, we have studied an extracellular zinc-metalloprotease (VemA) encoded by V. europaeus, which was identified as a vibriolysin, highly conserved in this species and homologous in other pathogenic and non-pathogenic species. Virulence challenge experiments demonstrated that infection processes were faster when Manila clam larvae and juveniles were infected with the wildtype rather than with a mutant defective in the vemA gene (ΔvemA). V. europaeus was able to resist the bactericidal action of mucus and displayed a chemotaxis ability favoured by VemA to colonize the body mucus of clams and form a biofilm. The overall results suggest that VemA, although it is not a major virulence factor, plays a role in the colonization of the Manila clam mucus, and thus boosts the infection process as we observed in virulence challenge experiments.