Figure 4
The expression of tryptophanase and the production of indole in E. coli are not affected by ciprofloxacin treatment. (a) Single cell distributions of tryptophanase-GFP. Exponential-phase samples (OD600 = 0.15) from LB cultures of E. coli BW25113 (negative control) and BW25113 TnaA-GFP were analysed by flow cytometry (100,000 events per sample). The fluorescence distributions of GFP in the TnaA-GFP culture is shown before (positive control) and after (10, 20, 30, 40, 50 and 60 min) the addition of ciprofloxacin (100 × MIC). In agreement with a previous study31, all samples showed 3 distinct peaks implying sub-populations of cells with low, medium and high tryptophanase content (peaks indicated by black, blue and green vertical lines, respectively). (b) Indole concentration (µM) in the supernatant of exponential-phase samples (OD600 = 0.15) from LB cultures of E. coli BW25113 wild-type before (time zero) and after (1, 2, 3, 4 and 5 h) treatment with ciprofloxacin (100 × MIC). Indole was measured by the Kovacs assay after passing each sample through a C18 solid phase extraction column to concentrate indole tenfold. All data are the mean ± SD of three biological replicates.
