Evidence for siderophore‐dependent iron acquisition in group B streptococcus

Abstract

Summary Mutagenesis of group B streptococcus (GBS) withTn 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 (µ µ µ µ M) = = = = 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 wildtype 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.

Albomycin Uptake via a Ferric Hydroxamate Transport System ofStreptococcus pneumoniaeR6

“…The structure of E. coli FhuD with loaded substrate has been resolved at the atomic level and reveals recognition of the ferric hydroxamate center. Distinct structures are observed in substrate-loaded FhuD proteins com- (36), and a group B streptococcus (12). The fhuD fhuB fhuG fhuC genes of S. pneumoniae are transcribed in the same direction and most likely form an operon.…”

“…In the following, spr0934 will be designated fhuD, spr0935 fhuB, spr0936 fhuG, and spr0938 fhuC, (Fig. 3B) according to the nomenclature introduced by Clancy et al (12), who studied siderophore-dependent iron acquisition of a group B streptococcus. We refrained from using the pia gene nomenclature introduced by Brown et al (9) because the fhu designation specifically refers to ferric hydroxamate uptake, which we introduced for E. coli (26) and has been used since then for gram-negative and gram-positive bacteria (5,8,30,31).…”

“…In S. aureus the gene order is fhuC fhuB fhuG, whereas fhuD1 and fhuD2 are located at other sites on the chromosome (36). In the group B streptococcus all four genes have the same transcription polarity but are arranged fhuC fhuD fhuB fhuG (12). An iron transport system was studied in a clinical isolate of S. pneumoniae 0100993.…”

Transcriptional and Proteomic Profiles of Group B Streptococcus Type V Reveal Potential Adherence Proteins Associated with High-Level Invasion

“…Clancy et al (4) have now reported a siderophore (hydroxamate)-mediated iron transport system in GBS characterized by a FhuD siderophore receptor localized to the cell membrane. A polycistronic operon of four genes (fhuCDBG) putatively encodes an ATPase, cell surface receptor, and two transmembrane proteins, respectively (4).…”

The Delta Subunit of RNA Polymerase, RpoE, Is a Global Modulator ofStreptococcus mutansEnvironmental Adaptation

“…Interestingly, the putative ferrichrome transporter genes (SMU.995 to SMU.998) were induced in the ⌬rpoE strain under every condition, except to a smaller degree under oxidative stress. Sufficient levels of iron are necessary for bacterial survival and growth, but the accumulation of iron can lead to the production of toxic oxygen radicals via Fenton chemistry (17,76). Thus, its intracellular transport must be tightly controlled, and such induction might cause toxicity to the ⌬rpoE strain.…”