Plasmids mediating iron uptake in Vibrio anguillarum strains isolated from turbot in Spain

Vibrio strains isolated from diseased turbot in an experimental fish farm on the Atlantic coast of northwest Spain were identified as Vibrio anguillarum. The isolates shared many biochemical characteristics with V. anguillarum strains obtained from other sources, and harboured a plasmid species that showed extensive homology with plasmid pJM1, carried by V. anguillarum strain 775 isolated from an epizootic in North America. Restriction endonuclease analysis showed that the two plasmids were very similar albeit not identical. The presence of the plasmid in the turbot isolates was associated with their ability to cause disease in fish. Plasmid-carrying bacteria could also grow under conditions of iron limitation. Two outer membrane proteins, of 86 and 79 kDal, were induced, and a similar siderophore activity to that produced by V. anguillarum 775 was also detected under these conditions. The 86 kDal outer membrane protein cross-reacted immunologically with antiserum raised against the outer membrane protein OM2 produced by strain 775. Nonvirulent plasmidless derivatives were unable to grow under iron-limiting conditions, and were also unable to produce either siderophore activity or the 86 kDal outer membrane protein, suggesting the plasmid-mediated nature of these components.