FeoB-Mediated Uptake of Iron by Francisella tularensis

Abstract

ABSTRACTFrancisella tularensis, the bacterial cause of tularemia, infects the liver and replicates in hepatocytesin vivoandin vitro. However, the factors that govern adaptation ofF. tularensisto the intrahepatocytic niche have not been identified. Using cDNA microarrays, we determined the transcriptional profile of the live vaccine strain (LVS) ofF. tularensisgrown in the FL83B murine hepatocytic cell line compared to that ofF. tularensiscultured in broth. ThefslCgene of thefsloperon was the most highly upregulated. Deletion offslCeliminated the ability of the LVS to produce siderophore, which is involved in uptake of ferric iron, but it did not impair its growth in hepatocytes, A549 epithelial cells, or macrophages. Therefore, we sought an alternative means by whichF. tularensismight obtain iron. Deletion offeoB, which encodes a putative ferrous iron transporter, retarded replication of the LVS in iron-restricted media, reduced its growth in hepatocytic and epithelial cells, and impaired its acquisition of iron. Survival of mice infected intradermally with a lethal dose of the LVS was slightly improved by deletion offslCbut was not altered by loss offeoB. However, the ΔfeoBmutant showed diminished ability to colonize the lungs, liver, and spleen of mice that received sublethal inocula. Thus, FeoB represents a previously unidentified mechanism for uptake of iron byF. tularensis. Moreover, failure to produce a mutant strain lacking bothfeoBandfslCsuggests that FeoB and the proteins of thefsloperon are the only major means by whichF. tularensisacquires iron.