SIDEROPHORE PRODUCTION BY AEROMONAS-SALMONICIDA

Growth under conditions of iron-restriction and the production of siderophores was examined in 21 typical and 14 atypical strains of Aeromonas salmonicida. With the exception of one atypical strain, all strains grew and multiplied in the presence of the high-affinity iron chelators ethylenediamine di(0-hydroxyphenylacetic acid), alpha, alpha'-dipyridyl or transferrin. Chrome azurol S agar was used to screen bacterial strains growing under these conditions for the production of siderophores. Siderophore production was detected only in the typical strains. Siderophores were also detected in the iron-restricted culture supernatants of typical strains, where they were associated with an iron-binding activity. The siderophore was extracted from iron-restricted culture supernatant of one strain by adsorption onto an XAD-7 resin; it behaved as a 2,3-diphenol-catechol in several colorimetric assays. The results indicate that although both typical and atypical strains of A. salmonicida grow and multiply under conditions of iron-restriction, they use different iron-uptake mechanisms, siderophore-mediated and siderophore-independent, respectively. In cross-feeding assays, growth of typical strains was stimulated only by homologous iron-restricted supernatant, suggesting strain differences in the siderophore produced. However, one strain produced a culture supernatant with growth-stimulating activity for other typical and also atypical strains.