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Chapter 6 : Iron Requirements of and Acquisition of Iron by Legionella pneumophila
This chapter discusses the current understanding of the relationship between Legionella pneumophila and the metal iron. It summarizes the work of a number of laboratories that demonstrated the importance of iron for Legionella, and highlights recent advances toward uncovering mechanisms of L. pneumophila iron acquisition. The mutant displayed a 42% reduction in hemin binding, confirming that hbp potentiates hemin acquisition by L. pneumophila. Within U937 cells, NU216 and its allelic equivalent NU216R were approximately 100-fold more sensitive than the wild type to treatment with desferoxamine, confirming that they are defective for intracellular iron acquisition. The EDDA-hypersensitive mutant NU208 was also dramatically impaired for replication in U937 cells, and its infectivity defect was exacerbated by treatment of the macrophages with desferoxamine. A reconstruction of the NU208 mutation confirmed that the iron acquisition and infectivity defects were due to the transposon insertion and not a spontaneous second-site mutation. Sequence analysis demonstrated that the transposon disruption lies within a gene that is highly similar to the cytochrome c maturation gene, ccmC. ccmC is generally recognized for its role in the heme export step of cytochrome biogenesis. Quantitative infection assays demonstrated that NU229 was impaired ca. 80-fold in intracellular growth. Reconstruction of the mutant by allelic exchange proved that the defect was due to the inactivation of frgA and not a spontaneous second-site mutation. Subsequently, trans-complementation of the mutation demonstrated that the infectivity defect was directly due to the loss of FrgA.