Coxiella burnetii Exhibits Morphological Change and Delays Phagolysosomal Fusion after Internalization by J774A.1 Cells

Abstract

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. Measuring in vitro internalization of [35 S]methionine-[ 35 S]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.

Coxiella burnetiiSurvival in THP-1 Monocytes Involves the Impairment of Phagosome Maturation: IFN-γ Mediates its Restoration and Bacterial Killing

“…The impairment of cathepsin D accumulation reflects defective phagolysosomal fusion because lysosomal trackers did not accumulate in C. burnetii phagosomes. The lack of colocalization of C. burnetii and cathepsin D was not due to delayed acquisition of cathepsin D by C. burnetii vacuoles, which disagrees with a recent paper in which virulent C. burnetii delays phagolysosomal fusion in J774 cells (27), but these murine macrophage-like cells allow the replication of both virulent and avirulent organisms. In blood monocytes, in which only virulent C. burnetii organisms survive (Refs.…”

Is Q Fever an emerging or re-emerging zoonosis?

“…The passage of SCV to LCV in the host cell is well documented [66], but the stress at the origin of the formation of SCV and SDC have not yet been studied. So these markers of LCV or SCV could allow studying and identifying the external and cellular signals that trigger the differentiation of the bacteria.…”

“…This sigma factor may regulate genes involved in surviving stresses in metabolically active LCV [107]. Moreover, the small forms are able to delay phagolysosomal fusion, perhaps to facilitate the transition from SCV to LCV that occurs at pH 5.5 in the endosome [66]. The use of cellular markers (LAMP-1, EEA.1, rab7) [67,68] strongly suggests that the large replicative vacuoles containing Coxiella are derived from fusion with late endosomal-lysosomal organelles.…”

Uptake of Granulysin via Lipid Rafts Leads to Lysis of Intracellular Listeria innocua

“…and Coxiella spp. have evolved strategies to modify their intracellular compartments (51,52) or are known to escape from vesicular compartments to the cytosol-like L. monocytogenes (53). Mycobactera, for example, can stop phagosome maturation by inhibiting acquisition of the rab5 effector EEA-1.…”