A novel genomic island encodes vibrioferrin synthesis in the marine pathogen Photobacterium damselae subsp. damselae

In this study, we identified and analyzed a novel genomic island (GI), named pddGI-1, located on chromosome II of certain strains of the marine pathogen Photobacterium damselae subsp. damselae (Pdd). This GI shares structural similarities with other GIs found in Vibrio species, such as the Vibrio seventh pandemic island-II (VSP-II) of V. cholerae. The pddGI-1 island is a mosaic of gene blocks that encode functions related to ROS defense, anaerobic energy metabolism, and restriction-modification (RM) systems. Notably, pddGI-1 also includes a complete vibrioferrin siderophore system, enabling the bacteria to thrive in low-iron environments. Vibrioferrin was chemically identified from cell-free supernatants of Pdd RG91. Additionally, a pvsD mutant deficient in vibrioferrin biosynthesis was generated and analyzed. The results suggest that Pdd strains harbouring pddGI-1 gain a distinct growth advantage under iron-limited conditions. These findings, along with previous research, highlight the significant heterogeneity in iron assimilation systems among Pdd strains.