SIDEROPHORES AND RELATED OUTER-MEMBRANE PROTEINS IN VIBRIO SPP WHICH ARE POTENTIAL PATHOGENS OF FISH AND SHELLFISH

A total of eight reference strains and 43 environmental isolates of Vibrio species that are potential fish pathogens, were assayed for the production and utilization of siderophores. Chemical and biological assays indicated that all species produced phenolate compounds and only some strains of V. cholerae non-O1, V. parahaemolyticus and V. fluvialis produced hydroxamates. Bioassays indicated that all species produced compounds that stimulated the growth of the homologous and the heterologous species in low-iron media. The catechol-type siderophores produced may be functionally related to enterobactin as demonstrated by bioassays with enterobactin-deficient mutants. However, the chromatographic analysis and absorption spectra of supernatants and their extracts showed some differences among catechols excreted by Vibrio species. The hydroxamate compounds produced by some strains of V. fluvialis and V. parahaemolyticus were different from the aerobactin. The synthesis of iron-regulated outer membrane proteins was also examined in representative strains of each species. The molecular size of the main induced proteins ranged between 74 and 95 kDa, and were relatively species specific.