IRON ACQUISITION BY RENIBACTERIUM-SALMONINARUM - CONTRIBUTION OF IRONREDUCTASE

Renibacterium salmoninarum is the etiologic agent of bacterial kidney disease in salmonid fish. The virulence of R. salmoninarum has been as sociated with hydrophobicity although little is known of the means by which this organism acquires iron. In this study, 7 strains of R. salm oninarum were grown in iron-restricted media. Siderophore production w as not detected by chemical assays. The growth of all strains, but par ticularly non-hydrophobic strains, was considerably reduced in the pre sence of the high-affinity iron chelators ethylenediamine di(o-hydroxy phenylacetic acid) or alpha,alpha'-dipyridyl or when cultured in Chele x-treated medium. Culture supernatant from both hydrophobic and nonhyd rophobic strains was found to inhibit the binding of iron by bovine tr ansferrin and this inhibition was most pronounced in supernatants deri ved from iron-sufficient cultures. A strong iron reductase activity wa s detected in R. salmoninarum cells. Maximum reductase activity occurr ed under iron-restricted culture conditions with reduced beta nicotina mide adenine dinucleotide as reductant. The results suggest that iron reductase is an important component of the iron acquisition mechanism of R. salmoninarum.