Figure 7. Antibiotic Agents that Target Folate Biosynthesis Trigger ZTP Riboswitch-mediated Gene Expression.

(A) Agar diffusion assays of the E. coli WT riboswitch reporter strain described in Figure 6A. Blank discs were spotted with 5 µL of either 1 µg mL⁻¹ TMP, 400 µg mL⁻¹ sulfathiazole (SFT), 45 mg mL⁻¹ methotrexate (MTX), 4 µg mL⁻¹ kanamycin (Kan) or 5 µg mL⁻¹ chloramphenicol (CM), Disks infused with gentamycin (GE), rifamycin (RIF), tetracycline (TE), and imipenem (IPM) were purchased from BD. All plates contained M9 agar medium with X-gal.

(B) Plots of the relative β-galactosidase activity of the E. coli WT riboswitch reporter strain grown with various antibiotics as indicated. Concentrations tested are approximately one half log unit below the minimum inhibitory concentration (MIC) for each antibiotic, with the exception of methotrexate, which was tested at 100 µg mL⁻¹