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Evidence for siderophore‐dependent iron acquisition in group B streptococcus
Author(s) -
Clancy Anne,
Loar Jesse W.,
Speziali Craig D.,
Oberg Michael,
Heinrichs David E.,
Rubens Craig E.
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2005.04974.x
Subject(s) - siderophore , biology , operon , mutant , mutagenesis , plasmid , microbiology and biotechnology , bacterial outer membrane , transposable element , transmembrane protein , transposon mutagenesis , transmembrane domain , intracellular , biochemistry , escherichia coli , gene , receptor
Summary Mutagenesis of group B streptococcus (GBS) with Tn phoZ , a transposon designed to identify secreted protein genes, identified the gene homologues fhuD and fhuG . The encoded proteins participate in siderophore (hydroxamate)‐dependent iron(III) transport in other bacterial species. Sequence analysis of the genome determined that fhuD and fhuG are members of a polycistronic operon comprised of four genes, fhuCDBG , that encode a putative ATPase, cell surface receptor and two transmembrane proteins respectively. We hypothesized that FhuD was a siderophore receptor. Western analysis of cell extracts localized FhuD to the bacterial cell membrane. Fluorescence quenching experiments determined that purified FhuD bound hydroxamate‐type siderophores. FhuD displayed highest affinity for iron(III)‐desferroxamine, with a K D (µM) = 0.05, identical to that described for FhuD2 from Staphylococcus aureus . The role of Fhu in siderophore‐iron transport was also characterized. A fhu mutant, ACFhu1, was equally sensitive to the iron‐dependent antibiotic streptonigrin as the wild‐type strain, suggesting that ACFhu1 was not reduced for intracellular iron concentrations in the absence of exogenous siderophore. However, ACFhu1 transported significantly less siderophore‐bound iron in 55 Fe accumulation assays. These data provide the first evidence of siderophore‐mediated iron acquisition by GBS.