FIG 2 .
rrnB P1 promoter activity correlates with persisters independently of mRNA interferases and ppGpp. (A) Exponentially growing cells of MG1655-ASV carrying an rrnB P1::gfpunstable transcription fusion were exposed to 1-µg/ml ciprofloxacin for 4 h. The antibiotic-treated cells were then analyzed by FACS. The dim (5%), middle (20%), and total (100%) fractions of the population were isolated by cell sorting. Cells from the dim, middle, and total fractions of the population were sorted onto agar plates, and the persisters were quantified by CFU. (B) A representative plate image after sorting. (Top) One cell was sorted onto each spot from an exponentially growing culture without antibiotic challenge. (Bottom) One thousand cells were sorted onto each spot from a ciprofloxacin-challenged culture. (C) MG1655-ASV (WT), isogenic Δ10TA, and ΔrelA ΔspoT cultures were exposed to 1-µg/ml ciprofloxacin for 4 h and underwent FACS analysis and cell sorting. The percent survival for each fraction was determined by comparing the CFU count with the total number of sorted cells. Data are the average results from at least two independent experiments performed with three biological replicates (n ≥ 6). Error bars represent standard deviations. An asterisk indicates a significant difference (P < 0.05) by two-tailed Student’s t test.