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Infection and Immunity, July 2000, p. 3815-3821, Vol. 68, No. 7
Washington State University, Department of
Microbiology, Pullman, Washington 99164-4233
Received 27 January 2000/Returned for modification 14 February
2000/Accepted 1 April 2000
Coxiella burnetii, the etiological agent of Q fever, is
an obligate intracellular bacterium proliferating within the harsh environment of the phagolysosome. Mechanisms controlling trafficking to, and survival of pathogens within, the phagolysosome are unknown. Two distinct morphological variants have been implicated as playing a
role in C. burnetii survival. The dormant small-cell
variant (SCV) is resistant to extracellular stresses and the more
metabolically active large-cell variant (LCV) is sensitive to
environmental stresses. To document changes in the ratio of SCVs to
LCVs in response to environment, a protein specific to SCV, ScvA, was quantitated. During the first 2 h after internalization of
C. burnetii by J774A.1 cells, the level of ScvA decreased,
indicating a change from a population containing primarily SCVs to one
containing primarily LCVs. In vitro experiments showed that 2 h of
incubation at pH 5.5 caused a significant decrease in ScvA in contrast
to incubation at pH 4.5. Measuring in vitro internalization of
[35S]methionine-[35S]cysteine in response
to pH, we found the uptake to be optimal at pH 5.5. To explore the
possibility that after uptake C. burnetii was able to delay
phagolysosomal fusion, we used thorium dioxide and acid phosphatase to
label phagolysosomes during infection of J774A.1 cells. We determined
that viable C. burnetii was able to delay phagolysosomal
fusion. This is the first time that a delay in phagolysosomal fusion
has been shown to be a part of the infection process of this pathogenic microorganism.
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Coxiella burnetii Exhibits Morphological
Change and Delays Phagolysosomal Fusion after Internalization by
J774A.1 Cells
*
Corresponding author. Mailing address: University of
Wyoming, Department of Molecular Biology, Laramie, WY 82071-3944. Phone: (307) 766-3435. Fax: (307) 766-5098. E-mail:
dhowe{at}uwyo.edu.
This paper is dedicated to the memory of Louis P. Mallavia.
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