Iron-regulated outer membrane protein OM2 of Vibrio anguillarum is encoded by virulence plasmid pJM1

Vibrio anguillarum 775 harboring the virulence plasmid pJM1 synthesized an outer membrane protein of 86 kilodaltons, OM2, that was inducible under conditions of iron limitation. pJM1 DNA fragments obtained by digestion with restriction endonucleases were cloned into cosmid vectors and transferred into Escherichia coli. The OM2 protein was synthesized in E. coli, demonstrating that it is actually encoded by the pJM1 plasmid. Mobilization of the recombinant plasmids to V. anguillarum was accomplished by using the transfer factor pRK2013. A V. anguillarum exconjugant harboring the recombinant derivative pJHC-T7 and synthesizing the OM2 protein took up 55Fe3+ and grew under iron-limiting conditions, only in presence of the pJM1-mediated siderophore. Exconjugants harboring recombinant plasmids, such as pJHC-T2 which did not encode the OM2 protein, were transport negative. Membrane protein iodination experiments, together with protease treatment of whole cells, indicated that the OM2 protein is exposed to the outside environment of the V. anguillarum cells.