Investigation of the role of type IV pili in the virulence of Vibrio anguillarum towards sea bass (Dicentrarchus labrax L) larvae

Background: Vibriosis, caused by Vibrio anguillarum, is an important infectious disease affecting many economically important fish, bivalves and crustaceans. Although some virulence-related factors have already been identified in V. anguillarum, the virulence mechanisms of V. anguillarum still remain poorly understood. Genes encoding type IV pili have been identified as important virulence factors in several human, plant and animal pathogens, including fish pathogens such as Aeromonas salmonicida and Vibrio vulnificus. Objectives: The objective of this study was to investigate whether Type IV pili are involved in V. anguillarum virulence. Methods: Full genome sequencing of V. anguillarum strain VIB15, previously shown to be highly virulent towards sea bass larvae, revealed genes encoding two type IV pilus systems. The first system shows similarity to the V. vulnificus Pil system and the Aeromonas salmonicida Tap system, both involved in virulence. The other type IV pilus system shows homology to the mannose-sensitive hemagglutinin pilus of Vibrio cholerae. In order to examine the putative role of the Pil system in V. anguillarum virulence, a pilA mutant of strain VIB15 was constructed and its pathogenicity was assessed in a gnotobiotic sea bass system developed for virulence screening. Conclusions: Our results suggest that the V. anguillarum pilA gene is not crucial for virulence towards sea bass larvae. Possibly, the other type IV pilus can complement the pilA mutation. As such, further research on both type IV pilus systems identified in this pathogen is required to unravel the potential role of type IV pili in V. anguillarum virulence.status: publishe