Figure 6

(A,B) Persister cell formation upon limitation of tRNA charging in the strain lacking the 10 mRNase toxins (Δ10TA). Stationary phase MG1655valS^ts cells were diluted 1:500 and grown at 36.6 °C until OD₆₀₀ ~ 0.1 in a temperature-controlled microtiter plate reader. MG1655, MG1655Δ10TA, and MG1655valS^tsΔ10TA cells were used as controls. Cells were treated with 150 μg/ml ampicillin, and the optical density of the cultures was recorded over time (A). Colony forming units were counted before the treatment and 6 h and 16 h after treatment (B). Cells were treated with β-lactamase before plating on LB plates. Cultures marked with a star were shifted to room temperature for 5 minutes after 4 h of incubation and incubated for an additional ~2 h (until they reached OD₆₀₀ ~ 0.1) before ampicillin treatment. (C,D) Antibiotic survival of MG1655 ΔrelA ΔspoT stringent mutants in supplemented M9 medium (C) or LB medium (D). Stationary phase cultures of the indicated strains were diluted 1:100 into fresh medium and directly challenged with 100 μg/ml ampicillin. Colony forming units were determined over time for 24 h, revealing biphasic killing. Bar diagrams display average and standard deviation of bacterial survival after 24 h of treatment. The growth of all strains in both media is shown in Fig. S6.