Infection and Immunity, August 2000, p. 4498-4504, Vol. 68, No. 8
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
New Product Research Laboratories I, Daiichi Pharmaceutical Co., Ltd., Tokyo 134-8630, Japan
Received 11 February 2000/Returned for modification 13 April 2000/Accepted 8 May 2000
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.
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