Previous Article | Next Article ![]()
Infection and Immunity, September 1998, p. 4450-4460, Vol. 66, No. 9
Departments of
Microbiology1 and
Pathology,2 College of Physicians
and Surgeons, Columbia University, New York, New York 10032
Received 6 April 1998/Returned for modification 13 May
1998/Accepted 29 May 1998
During infection, the Legionnaires' disease bacterium,
Legionella pneumophila, survives and multiplies within a
specialized phagosome that is near neutral pH and does not fuse with
host lysosomes. In order to understand the molecular basis of this organism's ability to control its intracellular fate, we have isolated
and characterized a group of transposon-generated mutants which were
unable to kill macrophages and were subsequently found to be defective
in intracellular multiplication. These mutations define a set of 20 genes (19 icm [for intracellular multiplication] genes
and dotA [for defect in organelle trafficking]). In this report, we describe a quantitative assay for phagosome-lysosome fusion
(PLF) and its use to measure the levels of PLF in cells that have been
infected with either wild-type L. pneumophila or one of
several mutants defective in different icm genes or
dotA. By using quantitative confocal fluorescence
microscopy, PLF could be scored on a per-bacterium basis by determining
the extent to which fluorescein-labeled L. pneumophila
colocalized with host lysosomes prelabeled with rhodamine-dextran.
Remarkably, mutations in the six genes that were studied resulted in
maximal levels of PLF as quickly as 30 min following infection. These
results indicate that several, and possibly all, of the icm
and dotA gene products act at an early step during
phagosome establishment to determine whether L. pneumophila-containing phagosomes will fuse with lysosomes.
Although not ruled out, subsequent activity of these gene products may
not be necessary for successful intracellular replication.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Early Events in Phagosome Establishment Are
Required for Intracellular Survival of Legionella
pneumophila

and
*
Corresponding author. Mailing address: Department of
Microbiology, College of Physicians and Surgeons, Columbia University, 701 West 168th St., New York, NY 10032. Phone: (212) 305-6913. Fax:
(212) 305-1468. E-mail:
shuman{at}cuccfa.ccc.columbia.edu.
Present address: Department of Medicine, Nephrology Section,
Indiana University Medical Center, Indianapolis, IN 46202.
Present address: Department of Biochemistry, Cornell University
Medical College, New York, NY 10021.
This article has been cited by other articles:
| J. Bacteriol. | J. Virol. | Eukaryot. Cell |
|---|
| Microbiol. Mol. Biol. Rev. | Clin. Vaccine Immunol. | All ASM Journals |
|---|