The effect of iron limitation growth conditions on the cell and extracellular components of the fish pathogen Pasteurella piscicida

The effect of iron limitation, using the iron-chelating agent 2,2 dipyridyl, on the electrophoretic profiles of outer membrane proteins (OMPs) and extracellular products (ECPs) from 21 Pasteurella piscicida strains isolated from Europe and Japan was investigated. In addition, the effect of iron-limited and iron-surplus growth conditions on caseinase activity in culture supernatants of the pathogen was examined. The majority of P. piscicida strains, from Greece, Italy and France, cultured under iron-limited conditions, produced four novel OMPs (63 and three at and above 200 kDa). In contrast, iron-regulated outer membrane proteins were not induced in Japanese strains. Electrophoretic analysis of the ECPs from the pathogen grown under iron surplus and iron limitation revealed a large range of products and additional high molecular mass (MM) bands were evident under iron-limited conditions. When culture supernatants were analysed for their activity, most of the bacteria tested showed elevated activities under iron limited conditions. Finally, neither hydroxamate nor phenolate type siderophores could be detected with any of the chemical assays used.