Bacterial cyclic β‐(1,2)‐glucans sequester iron to protect against iron‐induced toxicity

Cellular iron homeostasis is critical for survival and growth. Bacteria employ a variety of strategies to sequester iron from the environment and to store intracellular iron surplus that can be utilized in iron‐restricted conditions while also limiting the potential for the production of iron‐induced reactive oxygen species (ROS). Here, we report that membrane‐derived oligosaccharide (mdo) glucan, an intrinsic component of Gram‐negative bacteria, sequesters the ferrous form of iron. Iron‐binding, uptake, and localization experiments indicated that both secreted and periplasmic β‐(1,2) ‐ glucans bind iron specifically and promote growth under iron‐restricted conditions. Xanthomonas campestris and Escherichia coli mutants blocked in the production of β‐(1,2) ‐ glucan accumulate low amounts of intracellular iron under iron‐restricted conditions, whereas they exhibit elevated ROS production and sensitivity under iron‐replete conditions. Our results reveal a critical role of glucan in intracellular iron homeostasis conserved in Gram‐negative bacteria.