Small Molecule Inhibitors of the Bacterioferritin (BfrB)–Ferredoxin (Bfd) Complex Kill Biofilm-Embedded Pseudomonas aeruginosa Cells

[Image: see text] Bacteria depend on a well-regulated iron homeostasis to survive adverse environments. A key component of the iron homeostasis machinery is the compartmentalization of Fe(3+) in bacterioferritin and its subsequent mobilization as Fe(2+) to satisfy metabolic requirements. In Pseudomonas aeruginosa Fe(3+) is compartmentalized in bacterioferritin (BfrB), and its mobilization to the cytosol requires binding of a ferredoxin (Bfd) to reduce the stored Fe(3+) and release the soluble Fe(2+). Blocking the BfrB-Bfd complex in P. aeruginosa by deletion of the bfd gene triggers an irreversible accumulation of Fe(3+) in BfrB, concomitant cytosolic iron deficiency and significant impairment of biofilm development. Herein we report that small molecules developed to bind BfrB at the Bfd binding site block the BfrB-Bfd complex, inhibit the mobilization of iron from BfrB in P. aeruginosa cells, elicit a bacteriostatic effect on planktonic cells, and are bactericidal to cells embedded in mature biofilms.