Evidence for siderophore-dependent iron acquisition in group B streptococcus.
Mutagenesis of group B streptococcus (GBS) with TnphoZ, 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) (microM) = 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.
Clancy
Anne
A
Division of Infectious Diseases, Immunology, and Rheumatology, Department of Pediatrics, Children's Hospital and Regional Medical Center/University of Washington, 307 Westlake Avenue N, Seattle, 98109, USA. anne.clancy@seattlechildrens.org
Loar
Jesse W
JW
Speziali
Craig D
CD
Oberg
Michael
M
Heinrichs
David E
DE
Rubens
Craig E
CE
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D017931:DNA Primers; D007501:Iron / Q000378:metabolism*; D008969:Molecular Sequence Data; D009876:Operon; D017386:Sequence Homology, Amino Acid; D017262:Siderophores / Q000378:metabolism*; D013292:Streptococcus agalactiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D013308:Streptonigrin
D001426:Bacterial Proteins; D017931:DNA Primers; D017262:Siderophores; D013308:Streptonigrin; D007501:Iron