GROWTH-INHIBITION OF THE SALMON PATHOGEN VIBRIO-ORDALII BY A SIDEROPHORE PRODUCED BY VIBRIO-ANGUILLARUM STRAIN VL4355

Thirty strains of V. anguillarum were tested for the production of inh ibitory substances against closely-related bacteria using the deferred antagonism test. Only one strain, Vibrio anguillarum VL4355, inhibite d strains of V. ordalii and this effect was blocked by the addition of iron salts to the culture medium. Siderophore production was investig ated for this strain. Results from bioassays suggested that strain VL4 355 produced a siderophore related to anguibactin, the plasmid-encoded phenolate siderophore produced by V. anguillarum strain 775. However, when plasmid DNA was compared for strains 775 and VL4355 the BamHI-ge nerated restriction profiles were different, although hybridization ex periments indicated some homology. Using the chrome-azurol sulphate as say to measure siderophore production, strain VL4355 yielded significa ntly higher values than other V. anguillarum strains. Amberlite XAD-2 was used to produce concentrated siderophore preparations from strains VL4355 and 775. Both preparations were inhibitory to the growth of st rains of V. ordalii, but not V. anguillarum, as were solutions of the iron chelator ethylenediamine-di(o-hydroxyphenylacetic acid). The diff erence in sensitivity to iron-limiting conditions for V. ordalii and V . anguillarum, coupled with the inability of V. ordalii to utilize fer ric-anguibactin, could reflect different mechanisms of iron uptake for these two organisms.