Characterization of the High-Pathogenicity Island encoding the siderophore piscibactin in Vibrio anguillarum: effects on bacterial virulence and implications for the control of vibriosis in fish

Abstract

Vibrio anguillarum is a marine pathogen that can infect warm- and coldwater fish with economical importance in aquaculture. One of the main virulence factosr of this organism is the synthesis and utilization of siderophores, molecules able to bind iron with high affinity from the environment and/or host tissues. Two siderophore-mediated systems have been described: a system that encodes vanchrobactin (encoded in the chromosome and present in all pathogenic strains) and another that encodes anguibactin (encoded in the plasmid pJM1 and present in serotype O1 strains). The vanchrobactin biosynthesis and transport genes are present in all strains but the expression is inactivated in strains that harbour the plasmid pJM1. Recently, genome analysis of V. anguillarum strain RV22 (vanchrobactin producer) revealed the presence of a gene cluster homologous to the Photobacterium damselae subsp. piscicida irp cluster that encodes the siderophore piscibactin. This observation rises the hypothesizes that RV22 could produce a piscibactin-like siderophore in addition to vanchrobactin. Therefore, the present work will focus on the mechanism involved in piscibactin biosynthesis, transport and regulation and its contribution to fish virulence. The regulation of the biosynthesis and secretion of both siderophores will be also studied. Furthermore, we will assess the contribution of vanchrobactin and piscibactin to the virulence of V. anguillarum. Vanchrobactin has been extensively studied, and the genes involved in its biosynthesis and transport have been established, but there are many regulatory aspects still unknown. However not much is known about piscibactin because it is the main siderophore of Pdp, a bacterium that is highly difficult to manipulate genetically. Therefore, we will study the molecular mechanisms involved in its biosynthesis, transport and regulation in V. anguillarum and the contribution of piscibactin to the virulence, persistence and dissemination of this pathogen in the host. Finally, we will evaluate the potential use of vanchrobactin and piscibactin outer membrane receptors as vaccines for use in aquaculture systems.