Vibrio vulnificus biotype 3 multifunctional autoprocessing RTX toxin is an adenylate cyclase toxin essential for virulence in mice

Vibrio vulnificus is an environmental organism that causes both food-borne and wound infections with high morbidity and mortality in humans. The annual incidence and global distribution of infections associated with this pathogen are increasing with climate change. In the late 1990s, an outbreak of tilapia-associated wound infections in Israel was linked to a previously unrecognized variant of V. vulnificus designated biotype 3. The sudden emergence and clonality of the outbreak suggest that this strain may be a true newly emergent pathogen with novel virulence properties compared to those of other V. vulnificus strains. In a subcutaneous infection model to mimic wound infection, the multifunctional autoprocessing RTX (MARTX) toxin of biotype 3 strains was shown to be an essential virulence factor contributing to highly inflammatory skin wounds with severe damage affecting every tissue layer. We conducted a sequencing-based analysis of the MARTX toxin and found that biotype 3 MARTX toxin has an effector domain structure distinct from that of either biotype 1 or biotype 2. Of the two new domains identified, a domain similar to Pseudomonas aeruginosa ExoY was shown to confer adenylate cyclase activity on the MARTX toxin. This is the first demonstration that the biotype 3 MARTX toxin is essential for virulence and that the ExoY-like MARTX effector domain is a catalytically active adenylate cyclase.