Bacterial cyclic ß-(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 ß-(1,2)-glucans bind iron specifically and promote growth under iron-restricted conditions. Xanthomonas campestris and Escherichia coli mutants blocked in the production of ß-(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.

Cell-cell signalling promotes ferric iron uptake in Xanthomonas oryzae pv. oryzicola that contribute to its virulence and growth inside rice.

Cell-cell communication mediated by diffusible signal factor (DSF) plays an important role in virulence of several Xanthomonas group of plant pathogens. In the bacterial pathogen of rice, Xanthomonas oryzae pv. oryzicola, DSF is required for virulence and in planta growth. In order to understand the role of DSF in promoting in planta growth and virulence, we have characterized the DSF deficient mutant of X. oryzae pv. oryzicola. Mutant analysis by expression analysis, radiolabelled iron uptake studies and growth under low-iron conditions indicated that DSF positively regulates ferric iron uptake. Further, the DSF deficient mutant of X. oryzae pv. oryzicola exhibited a reduced capacity to use ferric form of iron for growth under low-iron conditions. Exogenous iron supplementation in the rice leaves rescued the in planta growth deficiency of the DSF deficient mutant. These data suggest that DSF promotes in planta growth of X. oryzae pv. oryzicola by positively regulating functions involved in ferric iron uptake which is important for its virulence. Our results also indicate that requirement of iron uptake strategies to utilize either Fe(3+) or Fe(2+) form of iron for colonization may vary substantially among closely related members of the Xanthomonas group of plant pathogens.