Requirement of the Pseudomonas aeruginosa tonB gene for high-affinity ironacquisition and infection

To investigate the contribution of the TonB protein to high-affinity iron a cquisition in Pseudomonas aeruginosa, we constructed tonB-inactivated mutan ts from strain PAO1 and its derivative deficient in producing the sideropho res pyoverdin and pyochelin. The tonB mutants could not grow in a free-iron -restricted medium prepared by apotransferrin addition, even though the med ium 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. Intro duction of a plasmid carrying the intact tonB gene restored growth of the t onB mutant of PAO1 in the free-iron-restricted medium without any supplemen ts and restored growth of the tonB mutant of the siderophore-deficient deri vative in the medium supplemented with pyoverdin, pyochelin, hemoglobin, or hemin. In addition, animal experiments showed that, in contrast to PAO1, t he tonB mutant of PAO1 could not grow in vivo, such as in the muscles and l ungs of immunosuppressed mice, and could not kill any of the animals. The i n vivo growth ability and lethal virulence were also restored by introducti on 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 i ron acquisition may be essential for P. aeruginosa to infect the animal hos t.