The Apoptogenic Toxin AIP56 Is Secreted by the Type II Secretion System of Photobacterium damselae subsp. piscicida.

AIP56 (apoptosis-inducing protein of 56 kDa) is a key virulence factor of subsp. the causative agent of a septicaemia affecting warm water marine fish species. -associated pathology is triggered by AIP56, a short trip AB toxin with a metalloprotease A domain that cleaves the p65 subunit of NF-κB, an evolutionarily conserved transcription factor that regulates the expression of inflammatory and anti-apoptotic genes and plays a central role in host responses to infection. During infection by , AIP56 is systemically disseminated and induces apoptosis of macrophages and neutrophils, compromising the host phagocytic defence and contributing to the genesis of pathology. Although it is well established that the secretion of AIP56 is crucial for pathogenicity, the protein secretion systems operating in and the mechanism responsible for the extracellular release of the toxin remain unknown. Here, we report that encodes a type II secretion system (T2SS) and show that mutation of the EpsL component of this system impairs AIP56 secretion. This work demonstrates that has a functional T2SS that mediates secretion of its key virulence factor AIP56.