Requirement of the Pseudomonas aeruginosa tonB Gene for High-Affinity Iron Acquisition and Infection

Abstract

To investigate the contribution of the TonB protein to high-affinity iron acquisition in Pseudomonas aeruginosa, we constructed tonB-inactivated mutants from strain PAO1 and its derivative deficient in producing the siderophores pyoverdin and pyochelin. The tonB mutants could not grow in a free-iron-restricted medium prepared by apotransferrin addition, even though the medium was supplemented with each purified siderophore or with a heme source (hemoglobin or hemin). The tonB inactivation was shown to make P. aeruginosa unable to acquire iron from the transferrin with either siderophore. Introduction of a plasmid carrying the intact tonB gene restored growth of the tonB mutant of PAO1 in the free-iron-restricted medium without any supplements and restored growth of the tonB mutant of the siderophore-deficient derivative in the medium supplemented with pyoverdin, pyochelin, hemoglobin, or hemin. In addition, animal experiments showed that, in contrast to PAO1, the tonB mutant of PAO1 could not grow in vivo, such as in the muscles and lungs of immunosuppressed mice, and could not kill any of the animals. The in vivo growth ability and lethal virulence were also restored by introduction of the tonB-carrying plasmid in the tonB mutant. These results indicate clearly that the intact tonB gene-and, therefore, the TonB protein encoded by it-is essential for iron acquisition mediated by pyoverdin and pyochelin and via heme uptake in P. aeruginosa and suggest that the TonB-dependent iron acquisition may be essential for P. aeruginosa to infect the animal host.

Requirement of Staphylococcus aureus ATP-Binding Cassette-ATPase FhuC for Iron-Restricted Growth and Evidence that It Functions with More than One Iron Transporter

“…Indeed, inactivation of iron acquisition systems in S. aureus and many other bacteria can have a detrimental effect on virulence (3,9,14,18,24,30,38,(45)(46)(47)51), while the loss of some iron acquisition functions in some bacteria does not seem to affect virulence, probably due to redundancy of acquisition systems (29,38). For S. aureus, previous studies have demonstrated the importance of siderophore production for full virulence of the organism in a mouse model of infection (14), and Skaar et al have recently shown that heme acquisition by this bacterium is also important for virulence in mice (44).…”

Identification and characterization of an iron-regulated gene, chtA, required for the utilization of the xenosiderophores aerobactin, rhizobactin 1021 and schizokinen by Pseudomonas aeruginosa

“…Three TonB homologues, TonB1, TonB2 and TonB3, have been identified in the P. aeruginosa genome sequence and all three homologues have been experimentally characterized Takase et al, 2000;Zhao & Poole, 2000Huang et al, 2004). Siderophore-mediated iron transport in P. aeruginosa is primarily dependent on the activity of the TonB1 protein.…”

Revisiting quorum sensing: Discovery of additional chemical and biological functions for 3-oxo- N -acylhomoserine lactones

“…The P. aeruginosa genome contains many homologues of iron-siderophore receptor genes, reflecting the enormous flexibility of this organism to use various iron carriers. The ability to use such a wide variety of siderophores underscores the importance of iron for bacterial growth and survival as well as the need to compete with other microorganisms within the environments they inhabit for this essential metal (21,22).…”