3, scheme A. Since the iron-restricted growth of S. see more check details aureus Δsfa sbnA::Tc and S. aureus Δsfa sbnB::Tc mutants was restored in the presence of L-Dap, we hypothesized that this was due to the mutants’ renewed ability to synthesize staphyloferrin B. To verify this, we performed a chrome azurol S (CAS) assay on concentrated and methanol-extracted culture supernatants of several mutant derivatives of S. aureus Δsfa (grown under iron starvation) to quantify their

siderophore production (Figure 2B and 2C). Consistent with the growth phenotype illustrated in Figure 2A, amendment of growth media with L-Dap allowed siderophore production by S. aureus Δsfa sbnA::Tc and Δsfa sbnB::Tc (Figure 2C). Interestingly, supplementation

of the parental strain (Δsfa) with L-Dap enhanced the level of staphyloferrin B output by approximately five-fold (Figure 2C cf. Figure 2B). As a final method to demonstrate that the siderophore Y-27632 ic50 secreted by S. aureus Δsfa sbnA::Tc or Δsfa sbnB::Tc mutants, in media supplemented with L-Dap, was indeed staphyloferrin B, we performed plate-disk growth promotion assays by spotting culture supernatants onto sterile paper disks that were then placed onto TMS agar seeded with various S. aureus siderophore transport mutants (Figure 2D). Only culture supernatants from S. aureus sbnA::Tc or sbnB::Tc mutants that were fed L-Dap promoted the growth of seeded S. aureus Δhts and its isogenic wild-type strain, but strains containing a mutation in the sirA gene (encoding the receptor lipoprotein for staphyloferrin B) did not grow. Moreover, no growth-promoting siderophore was produced by sbnA or sbnB mutants grown in media Ceramide glucosyltransferase lacking L-Dap (Figure 2D). LC-ESI-MS/MS was used for confirmation of staphyloferrin B presence in methanol-extracted culture

supernatants of complemented mutants (data not shown); spectra were as published previously [17]. When iron-restricted growth media were supplemented with several other molecules that were predicted substrates or byproducts of an SbnA-SbnB reaction (e.g. L-ornithine, L-proline, and O-acetyl-L-serine) according to the models illustrated in Figure 3, scheme A, we noted that none rescued the iron-restricted growth of sbnA or sbnB mutants in the Δsfa background (Figure 2E). This leads us to conclude that none of these molecules can be modified into L-Dap by alternative S. aureus enzymes. Figure 3 Proposed schemes for SbnA- and SbnB-dependent synthesis of L-Dap. Scheme A is adapted from Thomas et al. [18] for which the functions of SbnA and SbnB are analogous to the proposed functions VioB and VioK, respectively. The proposed functions of SbnA in schemes B-D remain as a β-replacement enzyme while SbnB is proposed to be an NAD+-dependent dehydrogenase of the indicated amino acid.