Evidence for the role of a siderophore in promoting Vibrio anguillarum infections.

Vibrio anguillarum strain 775 harbouring the virulence plasmid pJM1 produces a plasmid-mediated siderophore that can crossfeed siderophore-deficient, receptor-proficient mutants of V. anguillarum in vitro. Experimental infections of salmonid fishes with mixtures consisting of the wild-type strain and a siderophore-deficient, receptor-proficient mutant resulted in recovery of both the wild-type and the mutant strain, while in infections with mixtures consisting of the wild-type strain and a siderophore-deficient, receptor-deficient mutant only the wild-type strain could be recovered. These results suggest that the V. anguillarum plasmid-mediated siderophore is produced in vivo in a diffusible form and that it is an important factor of virulence.