INSIGHTS INTO THE INTRACELLULAR LIFE-STYLE OF Bordetella pertussis

RODRÍGUEZ, M. EUGENIA; LAMBERTI YANINA; CAFIERO, HILARIO

Congreso; . LXV REUNIÓN ANUAL DE LA SOCIEDAD ARGENTINA DE INMUNOLOGÍA (SAI).; 2017

Bordetella pertussis (Bp), the causative agent of whooping cough, survives inside macrophages in mildly acidic compartments. In this study we show the role of several proteins involved in nutrient acquisition by Bp inside these cells. By shotgun proteomics we found that intracellular Bp has an overexpression of the outer membrane receptors BfrD and BfrE, involved in iron uptake from transferrin via host catecholamines. We further found that a ΔbfrDE mutant strain had a reduced intracellular survival inside THP-1 macrophages, suggesting that Bp may use catecholamines as a shuttle to acquire iron from transferrin. Confocal studies showing transferrin inside Bp phagosomes seem to support this hypothesis. The main periplasmic iron binding proteins of Bp are AfuA that binds Fe+3 and IRP1-3 that binds Fe+2, the latter ion being more stable at the phagosomal pH. Shotgun proteomics showed that the expression of AfuA is switched off in intracellular bacteria and this downregulation could be induced in vitro in bacteria growing at mildly acidic pH. Although our proteomic study failed to identify IRP1-3 in intracellular bacteria, this protein is induced under acidic in vitro conditions suggesting that Bp adapts to the phagosomal pH by expressing the best suited periplasmic iron binding proteins. We further found that MgtC promotes the growth of Bp at low pH as well as under magnesium starvation. A ΔmgtC strain had a diminished intracellular survival inside THP-1 cells, suggesting that this protein is involved in the adaptation to the conditions found by Bp inside the phagosome. This defect could be rescued by the addition of the vesicle pH neutralizing reagent Bailomycin A1 or an excess of Mg+2 to the cell culture medium. Altogether, these results show that through its evolution Bp has acquired an array of factors involved in nutrient uptake in the intracellular location, allowing this bacterium to adapt an intracellular lifestyle that promotes its persistence inside the host.