Reactivation of the vanchrobactin siderophore system of Vibrio anguillarum by removal of a chromosomal insertion sequence originated in plasmid pJM1 encoding the anguibactin siderophore system.

A chromosomal gene cluster encoding vanchrobactin biosynthesis and transport genes was identified in the Vibrio anguillarum serotype O1 strain, 775(pJM1), harbouring the anguibactin biosynthetic genes in the pJM1 plasmid. In this strain only anguibactin is produced as the vanchrobactin chromosome cluster has a RS1 transposition insertion into vabF, one of the vanchrobactin biosynthesis genes. Removal of this RS1 generating 775(pJM1)Delta tnp, still resulted in the detection of only anguibactin in specific bioassays. Surprisingly, when the pJM1 plasmid was not present as in the plasmidless strain H775-3, removal of the RS1 resulted in the detection of only vanchrobactin. These results thus can be interpreted as if presence of the pJM1 plasmid or of anguibactin itself is associated with the lack of detection of the vanchrobactin siderophore in bioassays. As high-performance liquid chromatography (HPLC) and mass spectrometry analysis demonstrated that both vanchrobactin and anguibactin were indeed produced in 775(pJM1)Delta tnp, it is clear that the pJM1-encoded anguibactin siderophore has higher affinity for iron than the vanchrobactin system in strains in which both systems are expressed at the same time. Our results underscore the importance of the anguibactin system in the survival of V. anguillarum 775 under conditions of iron limitation.