FIGURE 1.

Salicyl-capped mycobactin siderophore structure, genetic loci and first biosynthesis reaction. A, lipophilic MBT and hydrophilic cMBT share a common core structure but differ in the length of the alkyl substitution (R group). Atoms in blue are involved in the hexadentate ferric iron coordination. B, mbt-1 gene cluster produces mycobactin core, whereas mbt-2 gene cluster assembles and loads acyl fatty acid onto mycobactin lysine core. The black boxes indicate the presence of IdeR binding sequences, which cause genes repression upon iron binding on IdeR. C, adenylation-ligation reaction catalyzed by MbtA. ACP, acyl carrier protein domain of MbtB.