MgtE Homolog FicI Acts as a Secondary Ferrous Iron Importer in Shewanella oneidensis Strain MR-1.

The transport of metals into and out of cells is necessary for the maintenance of appropriate intracellular concentrations. Metals are needed for incorporation into metalloproteins but become toxic at higher concentrations. Many metal transport proteins have been discovered in bacteria, including the Mg transporter E (MgtE) family of passive Mg/Co cation-selective channels. Low sequence identity exists between members of the MgtE family, indicating that substrate specificity may differ among MgtE transporters. Under anoxic conditions, dissimilatory metal-reducing bacteria, such as and species, are exposed to high levels of soluble metals, including Fe and Mn Here we characterize SO_3966, which encodes an MgtE homolog in that we name FicI (errous ron and obalt mporter) based on its role in maintaining metal homeostasis. A SO_3966 deletion mutant exhibits enhanced growth over that of the wild type under conditions with high Fe or Co concentrations but exhibits wild-type Mg transport and retention phenotypes. Conversely, deletion of , which encodes an energy-dependent Fe importer, causes a growth defect under conditions of low Fe concentrations but not high Fe concentrations. We propose that FicI represents a secondary, less energy-dependent mechanism for iron uptake by under high Fe concentrations. MR-1 is a target of microbial engineering for potential uses in biotechnology and the bioremediation of heavy-metal-contaminated environments. A full understanding of the ways in which interacts with metals, including the means by which it transports metal ions, is important for optimal genetic engineering of this and other organisms for biotechnology purposes such as biosorption. The MgtE family of metal importers has been described previously as Mg and Co transporters. This work broadens that designation with the discovery of an MgtE homolog in that imports Fe but not Mg The research presented here also expands our knowledge of the means by which microorganisms have adapted to take up essential nutrients such as iron under various conditions.