A plasmid associated with virulence in the marine fish pathogen Vibrio anguillarum specifies an iron-sequestering system

Abstract

Many of the high-virulence strains of the marine fish pathogen Vibrio anguillarum isolated from epizootics of the widespread fish disease vibriosis, harbour a specific plasmid class which is absent from low-virulence strains¹. Curing experiments have confirmed a link between this specific plasmic class and the ability of V. anguillarum to establish infections². In general, all bacterial virulence factors promote growth in the antagonistic environment of the host defence mechanisms. One line of defence is provided by the proteins transferrin and lacto-ferrin^3–5, which bind iron, rendering it unavailable to pathogens. A mechanism whereby invading bacteria may successfully compete for the otherwise unavailable iron could therefore become crucial in enabling them to proliferate in body fluids and tissues. I report here evidence which shows that the V. anguillarum virulence plasmid specifies a very efficient iron-sequestering system enabling bacteria to survive in conditions of limited iron availability.