The etiologic agent of
Q fever Coxiella burnetii, is an intracellular obligate parasite that develops large vacuoles with phagolysosomal characteristics, containing multiple replicating bacteria. We have previously shown that Phase II C. burnetii replicative vacuoles generated after 24-48 h post
infection are decorated with the autophagic
protein LC3. The aim of the present study was to examine, at earlier stages of
infection, the distribution and roles of the
small GTPases Rab5 and Rab7, markers of early and late endosomes respectively, as well as of the
protein LC3 on C. burnetii trafficking. Our results indicate that: (i) Coxiella phagosomes (Cph) acquire the two Rab
proteins sequentially during
infection; (ii) overexpression of a dominant negative mutant form of Rab5, but not of Rab7, impaired Coxiella entry, whereas both Rab5 and Rab7 dominant negative mutants inhibited vacuole formation; (iii) Cph colocalized with the
protein LC3 as early as 5 min after
infection; acquisition of this
protein appeared to be a bacterially driven process, because it was inhibited by the bacteriostatic
antibiotic chloramphenicol and (iv) C. burnetii delayed the arrival of the typical lysosomal
protease cathepsin D to the Cph, which delay is further increased by
starvation-induced autophagy. Based on our results we propose that C. burnetii transits through the normal endo/phagocytic pathway but actively interacts with autophagosomes at early times after
infection. This intersection with the autophagic pathway delays fusion with the lysosomal compartment possibly favouring the intracellular differentiation and survival of the bacteria.