CONICET | Buscador de Institutos y Recursos Humanos

Intracellular bacterial pathogens depend on nutrients acquisition inside the host cells. By mean of proteomic studies we found that intracellular B. pertussis (Bp) changed the abundance of proteins involved in iron and magnesium uptake. Among iron related proteins, we found an over-expression of BfrD, BfrE, and Irp1-3, and a decrease of AfuA as compared with extracellular bacteria. Intracellular bacteria also express BP0414, a putative magnesium transporter with homology to MgtC. In this work, we show the role of these proteins in Bp adaptation to the intracellular environment. We had previously found that Bp is capable of surviving inside the host cells in mildly acidic compartments where it has access to transferrin. Real time PCR studies showed the down-regulation of afuA in bacteria growing in mildly acidic medium. Conversely, under these environmental conditions, irp1-3, bfrd, bfre, and mgtc were found up-regulated suggesting that the low pH is an environmental signal involved in the expression level of these genes. We found that a ΔbfrDE mutant strain had a reduced intracellular survival inside THP-1 macrophages, whereas the lack of Irp1-3 affected Bp survival only in the absence of BfrDE. These results suggest that BfrD and/or BfrE, two receptors implicated in iron uptake from transferrin via host catecholamines, are the main bacterial iron receptors inside the cell and that Irp1-3 might be relevant when this source of iron is scarce. 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 showed a reduced intracellular survival, which demonstrated to be related to 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