Figure 1.

SbnA and SbnB are essential for synthesis of staphyloferrin B in S. aureus. A) Chemical structure of staphyloferrin B with fundamental components labeled. Asterisks indicate ligands responsible for the octahedral coordination of iron. B) Within the sir-sbn genetic locus, the focus of this study is the characterization of mutations in sbnA (highlighted grey) (encoding a putative cysteine synthase) and sbnB (highlighted in black) (encoding a putative ornithine cyclodeaminase). Together, the products of these two genes are hypothesized to be an L-Dap synthase. C) S. aureus mutants were grown in chelex 100-treated TMS medium containing 10 μM holo-transferrin. In the Δsfa genetic background, growth in this medium is dependent on the production of the siderophore staphyloferrin B. Supplementation of the medium with FeCl₃ allows for equivalent growth for all strains (inset). D) The growth impairment exhibited by S. aureus sbnA or sbnB mutants, in the Δsfa genetic background, can be restored upon complementation in trans with a wild-type copy of the corresponding gene. Plasmid pALC2073 is the vehicle control.