Professional phagocytes, such as macrophages, employ different strategies to kill bacteria, including phagosome acidification, generation of reactive oxygen species and zinc poisoning, however the mechanisms underlying zinc accumulation inside phagosomes are not well understood. In their Research Article (Barisch et al, 2018), Caroline Barisch and co-workers use the soil amoeba Dictyostelium, which digests bacteria for nutrition, to monitor the fate of free zinc during phagocytosis of bacteria or latex beads using fluorescent probes. Immediately after particle uptake, zinc localises inside zincosomes that are of lysosomal and post-lysosomal nature, and in phagosomes. As shown for macrophages, zinc can also be delivered to the phagosomes of Dictyostelium through the fusion with zincosomes. The authors then analysed the localisation of the four Dictyostelium zinc transporters (Znt) to endosomes (ZntB), the contractile vacuole (ZntA) and the Golgi complex or recycling endosomes (ZntC, ZntD). Finally, the authors demonstrate that zinc poisoning results in the faster killing of a zinc-sensitive E. coli mutant that is deficient in the zinc efflux P-type ATPase ZntA, indicating that the accumulation of zinc in the phagosome contributes to bacteria killing. These findings suggest that zinc poisoning is an evolutionarily conserved process and might act in concert with other strategies to kill bacteria inside phagosomes.
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