Summary: The ability of and to utilize iron complexes, iron-proteins and exogenous microbial siderophores was evaluated. In a plate bioassay, all three species used not only ferric nitrate but also the iron chelates ferric citrate, ferric nitrilotriacetate and ferric 2,3-dihydroxybenzoate. Each species examined also used haemin, haemoglobin and haem-albumin as iron sources although only could acquire iron from transferrin or from haemoglobin complexed with haptoglobin. None of the haemophili obtained iron from ferritin or lactoferrin or from the microbial siderophores aerobactin or desferrioxamine B. However, the phenolate siderophore enterobactin supplied iron to both and , and DNA isolated from both organisms hybridized with a DNA probe prepared from the ferric enterobactin receptor gene In addition, a monospecific polyclonal antiserum raised against the 81 kDa ferric enterobactin receptor (FepA) recognized an iron-repressible outer membrane protein (OMP) in of between 80 and 82 kDa (depending on the strain). This anti-FepA serum did not cross-react with any of the OMPs of or . The OMPs of each species were also probed with antisera raised against the 74 kDa Cir or 74 kDa IutA (aerobactin receptor) proteins of Apart from one strain (NCTC 10665), in which an OMP of about 80 kDa cross-reacted with the anti-IutA sera, no cross-reactivity was observed between Cir, IutA and the OMPs of or . Thus, and possess a functional enterobactin iron-uptake system, and both siderophore-dependent and siderophore-independent high-affinity iron-sequestering systems are now known to be expressed in the genus .


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