RT Journal Article SR Electronic T1 Thiostrepton hijacks pyoverdine receptors to inhibit growth of Pseudomonas aeruginosa JF bioRxiv FD Cold Spring Harbor Laboratory SP 567990 DO 10.1101/567990 A1 Michael R. Ranieri A1 Derek C. K. Chan A1 Luke Yaeger A1 Madeleine Rudolph A1 Sawyer Karabelas-Pittman A1 Hamdi Abdo A1 Jessica Chee A1 Hanjeong Harvey A1 Uyen Nguyen A1 Lori L. Burrows YR 2019 UL http://biorxiv.org/content/early/2019/03/05/567990.abstract AB Pseudomonas aeruginosa is a biofilm-forming opportunistic pathogen and intrinsically resistant to many antibiotics. In a high-throughput screen for molecules that modulate biofilm formation, we discovered that the thiopeptide antibiotic, thiostrepton (TS) - considered inactive against Gram-negative bacteria - stimulated P. aeruginosa biofilm formation in a dose-dependent manner. This phenotype is characteristic of exposure to antimicrobial compounds at sub-inhibitory concentrations, suggesting that TS was active against P. aeruginosa. Supporting this observation, TS inhibited growth of a panel of 96 multidrug-resistant (MDR) P. aeruginosa clinical isolates at low micromolar concentrations. TS also had activity against Acinetobacter baumannii clinical isolates. Expression of Tsr - a 23S rRNA-modifying methyltransferase - in trans conferred TS resistance, confirming that the drug acted via its canonical mode of action, inhibition of ribosome function. Deletion of oligopeptide permease systems used by other peptide antibiotics for uptake failed confer TS resistance. TS susceptibility was inversely proportional to iron availability, suggesting that TS exploits uptake pathways whose expression is increased under iron starvation. Consistent with this finding, TS activity against P. aeruginosa and A. baumannii was potentiated by FDA-approved iron chelators deferiprone and deferasirox. Screening of P. aeruginosa mutants for TS resistance revealed that it exploits pyoverdine receptors FpvA and FpvB to cross the outer membrane. Our data show that the biofilm stimulation phenotype can reveal cryptic sub-inhibitory antibiotic activity, and that TS has activity against select multidrug resistant Gram-negative pathogens under iron-limited growth conditions, similar to those encountered at sites of infection.