FERRIC-REDUCTASE ACTIVITIES IN WHOLE CELLS AND CELL-FRACTIONS OF VIBRIO (LISTONELLA) ANGUILLARUM

The ability of Vibrio (Listonella) anguillarum strains from serotype g roups O1 and O2 to reduce Fe3+ in the form of different chelates was i nvestigated. All strains, grown in Mg minimal medium supplemented with 0.2 % Casamino acids, reduced Fe3+ complexed by citrate, nitrilotriac etic acid and EDTA. In whole cells, the degree of reduction was depend ent on the Fe3+ ligand and on the strain. with the greatest values cor responding to ferric dicitrate and serotype group O1 strains, respecti vely. The ferric-reductase activity increased, over the basal levels, when the cells were grown with iron added as ferric dicitrate, haemin oi haemoglobin. All strains also reduced ferricyanide, a compound that is not transported into the bacterial cells. Ferricyanide reduction w as also increased when the cells were grown in the presence of an iron source. All of the cell fractions (periplasm, membranes and cytoplasm ) showed Fe3+-reducing activity, with the highest values observed in t he presence of Mg2+, NADH and FAD in the assay buffer. Cytoplasmic fer ric-reductase could be visualized using native polyacrylamide or starc h gel electrophoresis. whereas the periplasmic and membrane reductase( s) could only be detected on starch gels. The results indicate the pre sence of different ferric-reductase activities in V. anguillarum, whic h could be involved in the different iron-acquisition systems present in this micro-organism, i.e. siderophore-mediated systems and sideroph ore-independent mechanisms.