The opportunistic marine pathogen <i>Vibrio parahaemolyticus</i> becomes virulent by acquiring a plasmid that expresses a deadly toxin

Significance Since 2009, an emergent shrimp disease, acute hepatopancreatic necrosis disease (AHPND), has been causing global losses to the shrimp farming industry. The causative agent of AHPND is a specific strain of Vibrio parahaemolyticus . We present evidence here that the opportunistic V. parahaemolyticus becomes highly virulent by acquiring a unique AHPND-associated plasmid. This virulence plasmid, which encodes a binary toxin [ V. parahaemolyticus Photorhabdus insect-related toxins (PirA vp and PirB vp )] that induces cell death, is stably inherited via a postsegregational killing system and disseminated by conjugative transfer. The cytotoxicity of the PirA vp /PirB vp system is analogous to the structurally similar insecticidal pore-forming Cry toxin. These findings will significantly increase our understanding of this emerging disease, which is essential for developing anti-AHPND measures.