Figure 2.

Supplementation of culture medium with L-Dap allows S. aureus sbnA and sbnB mutants to overcome the block in synthesis of staphyloferrin B. A) Bacterial growth curves in chelex 100-treated TMS containing 10 μM holo-transferrin as the sole iron source, with the indicated supplements. B) Siderophore quantification from culture supernatants of iron-starved S. aureus mutants via CAS assay (see Materials and Methods). The inset graph represents culture supernatants from identical strains but grown in medium supplemented with FeCl₃. Siderophore units are normalized to culture density. C) Same as in B) except culture media was supplemented with L-Dap. D) Siderophore-disk diffusion assays. Culture supernatants to be tested were derived from S. aureus Δsfa sbnA::Tc or Δsfa sbnB::Tc strains cultured in medium supplemented with, or without, L-Dap, as indicated, and were spotted onto sterile paper disks before being placed onto TMS agar plates seeded with S. aureus wild-type and siderophore transport mutants, as indicated. Plate disk bioassay is described in Materials and Methods. E) Bacterial growth curves for cultures of S. aureus Δsfa sbnA::Tc and S. aureus Δsfa sbnB::Tc mutants in chelex 100-treated TMS medium containing 10 μM holo-transferrin as the sole iron source, where the medium was supplemented with various hypothesized L-Dap synthase substrates and by-products from Fig. 3, scheme A.