Identification and characterization of fhuD1 and fhuD2, two genes involvedin iron-hydroxamate uptake in Staphylococcus aureus

Staphylococcus aureus can utilize several hydroxamate siderophores for grow th under iron-restricted conditions. Previous findings have shown that S. a ureus possesses a cytoplasmic membrane-associated traffic ATPase that is in volved in the specific transport of iron (III)-hydroxamate complexes. In th is study, we have identified two additional genes, termed fhuD1 and fhuD2, whose products are involved in this transport process in S. aureus. We have shown that fhuD2 codes for a posttranslationally modified lipoprotein that is anchored in the cytoplasmic membrane, while the deduced amino acid sequ ence predicts the same for fhuD1. The predicted FhuD1 and FhuD2 proteins sh are 41.0% identity and 56.4% total similarity with each other, 45.9 and 49. 1% total similarity with the FhuD homolog in Bacillus subtilis, and 29.3 an d 24.6% total similarity with the periplasmic FhuD protein from Escherichia coli. Insertional inactivation and gene replacement of both genes showed t hat while FhuD2 is involved in the transport of iron(III) in complex with f errichrome, ferrioxamine B, aerobactin, and coprogen, FhuD1 shows a more li mited substrate range, capable of only iron(III)-ferrichrome and iron (III) -ferrioxamine B transport in S. aureus. Nucleotide sequences present upstre am of both fhuD1 and fhuD2 predict the presence of consensus Fur binding se quences. In agreement, transcription of both genes was negatively regulated by exogenous iron levels through the activity of the S. aureus Fur protein .