The FeoA protein is necessary for the FeoB transporter to import ferrous iron

In many bacterial feo loci, the feoA gene is associated with the feoB gene. While the feoB-encoded FeoB protein has been demonstrated as a ferrous iron [Fe(II)] transporter, the function of the feoA gene product, FeoA, is unknown. In the present study, we report that the FeoA protein interacts with the FeoB Fe(II) transporter, which is required for FeoB-mediated Fe(II) uptake in Salmonella enterica. Iron uptake assay revealed that in the absence of FeoA, FeoB import of Fe(II) is impaired. Bacterial two-hybrid assay determined that the FeoA protein directly and specifically binds to the FeoB transporter in vivo. This FeoA-FeoB interaction appeared necessary for FeoB-mediated Fe(II) uptake because Salmonella expressing the mutant FeoA that cannot interact with FeoB failed to uptake Fe(II) via the FeoB transporter. Finally, we showed that the FeoA protein does not affect expression of the FeoB transporter per se.