is an important pathogen of bivalve mollusks worldwide. Several metalloproteases have been described as virulence factors in species of that are pathogenic to bivalves, but little is known about the contribution of these potential virulence factors to pathogenesis. In silico analysis of the genome of strain PP-145.98 led to the identification of two hitherto uncharacterized chromosomal loci encoding a probable vibriolysin-like metalloprotease and a putative collagenase, which were designated VnpA and ColA, respectively. Single defective mutants of each gene were obtained in PP-145.98, and the phospholipase, esterase and collagenase activities were studied and compared with those of the wild-type strain. The results showed that the single inactivation of resulted in a 3-fold reduction in phospholipase/esterase activity. Inactivation of reduced the collagenase activity by 50%. Finally, infection challenges performed in oyster larvae showed that Δ and Δ-single mutant strains of -are between 2-3-fold less virulent than the wild-type strain. Thus, the present work demonstrates that the production of both VnpA and ColA is required for the full virulence of the bivalve pathogen .