YERSINIA-RUCKERI PRODUCES 4 IRON-REGULATED OUTER-MEMBRANE PROTEINS BUT DOES NOT PRODUCE DETECTABLE SIDEROPHORES

The expression of iron-regulated outer membrane proteins (OMPs) was examined in 36 isolates of Yersinia ruckeri selected to represent a range of biotypes, serotypes and OMP-types. Iron-restricted growth was achieved in tryptone soya broth by chelation with 200-mu-M alpha,alpha'-dipyridyl, although similar results could be achieved with 25-mu-M transferrin or 280-mu-M ethylenediaminedihydroxyphenylacetic acid (EDDA). During growth under iron-restricted conditions, all 36 isolates produced four additional outer membrane proteins of molecular weights 72, 69.5, 68 and 66 kDa. Expression of these proteins was repressed by the addition of 100-mu-M FeCl3 to the growth medium, confirming that the proteins were iron-regulated. The facts that all of the isolates examined possessed the same four iron-regulated OMPs, and that the plasmid content of different serotypes is known to vary indicated that production of these proteins is probably chromosomally mediated and not plasmid-mediated. Production of siderophores was not detected in low iron media and suggested a direct iron-uptake mechanism for this organism.