Analysis of the aerobactin and ferric hydroxamate uptake systems of Yersinia pestis

Yersinia pestis genomes contain genes homologous to the aerobactin receptor (iutA) and biosynthetic genes (iucABCD) as well as the ferric hydroxamate uptake system (fhuCDB) of Escherichia coli. However, iucA is disrupted by a frameshift mutation. An E. coli strain carrying the cloned Y. pestis aerobactin region was unable to produce aerobactin, but could use the siderophore as an iron source. Repair of the frameshift mutation in iucA did not allow aerobactin production in E coli or Y. pestis. In contrast, a Y. pestis strain with a plasmid encoding the iucABCD-iutA genes from Shigella flexneri or pCoIV-K30 did produce and secrete the siderophore. In addition, Yersinia pseudo tuberculosis PB1, which encodes the iucABCD-iutA locus without the Y. pestis-specific frameshift mutation, also failed to produce aerobactin. The Y. pestis fhuCDB operon, encoding an ABC transporter for a range of hydroxamate siderophores, was able to complement a strain of E coli with a transposon insertion in fhuC, allowing utilization of aerobactin and ferrichrome. Y. pestis KIM6, a strain deficient in the production of the siderophore yersiniabactin, was able to use both the ferrichrome and the aerobactin siderophores as a source of iron. Mutations in iutA or the fhu operon abolished the ability of KIM6 to use aerobactin. Mutations in the fhu operon, but not in iutA, affected the ability of KIM6 to use ferrichrome. This demonstrates that Y. pestis uses both ferrichrome and aerobactin, but has lost the ability to synthesize aerobactin.