The phagosomal pH shapes B. pertussis intracellular survival

JUAN HILARIO CAFIERO; YANINA LAMBERTI; MARIA EUGENIA RODRIGUEZ

Bruselas

Simposio; 12th International Symposium on Bordetella; 2019

International Bordetella Society

Although Bordetella pertussis (Bp) has been historically considered an extracellular pathogen, recent studies showed that Bp survives inside different host cells and, particularly inside macrophages, it persists in mildly acidic compartments. In this work, we describe four proteins involved in the bacterial intracellular survival, some of them described for the first time for this pathogen. By mean of shotgun proteomic studies we found that intracellular Bp overexpresses the outer membrane receptors BfrD and BfrE, implicated in iron uptake from transferrin via host catecholamines. We, furthermore, found that a ΔbfrDE mutant strain had a reduced intracellular survival inside THP-1 macrophages, suggesting catecholamines may be facilitating the iron acquisition of intracellular Bp by shuttling iron from transferrin to this bacterium. Confocal studies showing transferrin inside Bp phagosomes support this hypothesis. The main periplasmic iron binding proteins of Bp are IRP1-3 that binds Fe(II) and AfuA, that binds Fe(III).. Shotgun proteomics showed that the expression of AfuA is switched off in intracellular bacteria. We found that this downregulation is induced by mildly acidic pH. Conversely, under these environmental conditions, IRP1-3 is upregulated. Studies using a ΔbfrDEΔIRP1-3 mutant further confirmed the IRP1-3 involvement in the bacterial iron uptake inside the cells suggesting that Bp adapts to environmental pH by expressing the best suited periplasmic iron binding proteins. We further found that Bp adaptation to the mildly acidic conditions found inside phagosomes also requires MgtC, a factor found required to promote Bp growth under low pH an/or magnesium starvation. A ΔmgtC strain had a diminished intracellular survival, and this defect could be rescued by the addition of the vesicle neutralizing reagent Bafilomycin A1, Our results showed a central role of MgtC in the bacterial ATP homeostasis in acidic environments. The results of this study constitute the first insights into the intracellular lifestyle of Bordetella pertussis