Metal economy in host-microbe interactions

HOST NUTRITIONAL IMMUNITY: DEPRIVING OR POISONING To date, the implication of divalent metals have been described in two different immune strategies that aim to fight microbial invaders. One consists in depriving microbes of essential divalent metals whereas the other aims at overloading invaders with toxic concentrations of metal. The contributions in this section present, in different situations, various aspects of this metal economy at the host-microbe interface. Two papers deal with metal homeostasis as hosts interact with bacteria. Diaz-Ochoa et al. (2014) review immunological mechanisms to sequester Fe, Mn, and Zn in the inflamed gut and strategies of commensals and pathogens to evade mucosal defenses and obtain such nutrients. Lisher and Giedroc (2013) detail chemical and structural mechanisms to capture Mn, an antioxidant used by pathogens to adapt to human hosts, and the impact of Fe and Zn on Mn bioavailability during infections. The most coveted metal, iron is key to nutritional immunity and microbial virulence. Using amoeba as model phagocyte, Bozzaro et al. (2013) present the tug of war between a bacterial predator, sequestering intracellular iron to resist invasion, and pathogens which elude such defense mechanisms. On mammalian defense against intracellular bacteria and protozoan parasites, Silva-Gomes et al. (2013) outline divergent approaches: iron-withholding to prevent microbial replication or iron-based oxidative injury to kill invaders. Host may also target invaders with toxic doses of Cu and Zn, normally kept at low concentrations. Neyrolles et al. (2013) present an opinion article on bacterial Zn and Cu poisoning in the context of Mycobacterium tuberculosis infection. Chaturvedi and Henderson (2014) summarize the specific properties of copper and its toxic effect on bacteria cells. Arguello et al. (2013) review how bacteria integrate homeostatic mechanisms to avoid Cu toxicity by sensing and regulating ion chelation, chaperoning and membrane transport.