Figure 6.

Model of F.n.n. infection course in Dictyostelium wt, Δnramp1, and ΔnrampB cells over 48 hpi. In wt cells, Nramp1 associates with the F.n.n.-phagosome but is removed from the compartment after 2 hpi dependent on IglC. At 6 hpi, most bacteria escaped the phagosome into the cytosol where they upregulate bacterial iron transporters for ferrous and ferric iron and start replicating. In nramp knockout cells, F.n.n. reaches its replicative niche earlier and more efficiently than in wt cells and subsequently more bacteria contribute to the bacterial burden. The bacteria respond to the lower cellular iron levels of the nramp mutants by an increased upregulation of iron uptake factors. NrampB is localized exclusively at the contractile vacuole and might therefore control phagosomal maturation and F.n.n. escape from the phagosome through regulation of global cellular iron homeostasis.