Iron at the host-microbe interface.

Iron is an essential micronutrient for nearly all living organisms. In addition to facilitating redox reactions, iron is bound by metalloproteins that participate in a variety of biological processes. As the bioavailability of free iron in host environments is extremely low, iron lies at the center of a battle for nutrients between microbes and their host. Mucosal surfaces such as the respiratory and gastrointestinal tracts are constantly exposed to commensal and pathogenic microorganisms. Whereas a key strategy of mammalian antimicrobial defense is to deprive microbes of iron, pathogens and some commensals have evolved effective strategies to circumvent iron limitation. Here we provide an overview of mechanisms underpinning the tug-of-war for iron between microbes and their host, with a particular focus on mucosal surfaces.