Iron acquisition by Renibacterium salmoninarum:contribution of iron reductase

Renibacterium salmoninarum is the etiologic agent of bacterial kidney disease in salmonid fish. The virulence of R. salmoninarum has been associated with hydrophobicity although little is known of the means by which this organism acquires iron. In this study, 7 strains of R. salmoninarum were grown in iron-restricted media. Siderophore production was not detected by chemical assays. The growth of all strains, but particularly non-hydrophobic strains, was considerably reduced in the presence of the high-affinity iron chelators ethylenediamine di(o-hydroxyphenylacetic acid) or alpha , alpha '-dipyridyl or when cultured in Chelex-treated medium. Culture supernatant from both hydrophobic and nonhydrophobic strains was found to inhibit the binding of iron by bovine transferrin and this inhibition was most pronounced in supernatants derived from iron-sufficient cultures. A strong iron reductase activity was detected in R. salmoninarum cells. Maximum reductase activity occurred under iron-restricted culture conditions with reduced beta nicotinamide adenine dinucleotide as reductant. The results suggest that iron reductase is an important component of the iron acquisition mechanism of R. salmoninarum.