Figure 1.

Identification of growth phases and image analysis of cultures. Panel A, Growth curve for L. innocua NCTC 11288 grown in TSB at 37 °C (n = 3 independent experimental measurements per point). The lag phase lasted for approximately 150 min (------); exponential phase (untreated cultures) began at about 150 min and by 400 min the cells were in the stationary phase. In cultures treated with RIF, stationary phase was induced immediately although some growth was still detected for ~120 min. Samples in panels B and C (untreated controls) were collected after 240 and 360 min and sample in panel C was collected 240 min after RIF administration (at 480 min). Panels B–D show light and fluorescence micrographs of L. innocua; for fluorescent imaging samples were stained with Nile red (1000 × magnification; scale bar = 1 µm). A graph of the distribution of cell lengths is shown for each sample with Gaussian distribution (red line). Data represents 180–200 cells from at least three images from four independent cultivations. The Box plots show medians, 50% of data in the range (box), non-outliers range (whiskers) and outliers (circles and stars). Sample B is representative of cells in exponential phase growth (240 min after inoculation) with the majority of cells appearing to be in the B period (>80% synchrony; mean = 1.34 µm, ± 0.29 µm). Sample C is representative of cells at the end of the exponential phase (360 min after inoculation) and represents the B period of older cultures (>80% synchrony; mean = 1.22 µm, ±0.26 µm). Sample D is representative of cells arrested at the C/D boundary by RIF (80-90% synchrony; mean = 1.92 µm, ±0.44 µm). Only 6.7% of cells in the C/D boundary samples are as short or shorter than those seen to predominate in the untreated samples (t-test, p =  < 0.01).