Vibrio coralliilyticus

Pathogenicity and virulence factors

Vibrio coralliilyticus is a causative agent of both bacterially induced coral bleaching and larval oyster mortality. In corals this bleaching is the result of the death of endosymbiont colonies which is mediated by V. coralliilyticus disabling Photosystem II and in some cases causing cell lysis. This also seems to be exacerbated by increased virulence as a result of increasing ocean temperatures. In oyster larvae an outbreak of V. coralliilyticus in a hatchery can result in mortality of up to 80%, greatly reducing hatchery production for that season leading to significant economic loss. In oysters the pathogen can cause deformities of the cilia as well as disfigurements of the velum, and eventually death. V. coralliilyticus also kills bacterial cells as well utilizing a Type VI secretion system to kill competitors, even out competing Vibrio cholerae cells in a bacterial killing assay. V. coralliilyticus possesses a host of virulence factors that contribute to its pathogenicity. It has been found to utilize several proteases, secretion systems, hemolysins, resistance factors, and quorum sensing. Some of the known proteases, zinc-metalloproteases, cause the previously mentioned inactivation of Photosystem II in coral photosynthetic endosymbionts (Symbiodinium) leading to coral beaching. Known secretion systems include Type III, Type IV and Type VI. Spinard et al. made note of several metalloprotease and hemolysin genes in the draft genome sequence published in 2015, several of which resembled proteins of known function found in a related pathogen, Vibrio anguillarum.