• Figure 2.
    Download figureOpen in new tabFigure 2. Memory and reset of colony-size bimodality.

    (A) Scheme of the experimental procedure for measuring the stability of colony morphotypes: Colonies of EPEC grown on LB agar were picked 1000 min after plating, resuspended, re-plated on LB agar, and subjected to ScanLag analysis. (B) Histogram of the fraction of colonies detected at each time point for bacteria taken from a SMALL colony. (C) Histogram of the fraction of colonies detected at each time point for bacteria taken from a BIG colony. (BC) Experiments were repeated in at least four independent biological replicates. (D, E) The same procedure was repeated for four consecutive cycles using bacteria taken from (D) SMALL or (E) BIG colonies, and in each cycle the fraction of BIG and SMALL colonies was determined. Data are presented as the means ± s.d. of five technical replicates. (F) Scheme of the experimental procedure for the ‘reset’ of the bimodality. (G) SMALL or (H) BIG colonies of EPEC were picked 1000 min after plating, resuspended in LB broth and grown overnight to stationary phase at 37°C. Cultures were then plated and subjected to ScanLag analysis.

    DOI: http://dx.doi.org/10.7554/eLife.19599.006

    Figure 3.
    Download figureOpen in new tabFigure 3. Model and measurements of bimodal switching rates.

    (A) Scheme and equations of a bimodal switching model. The two morphotypes, BIG and SMALL, are characterized by different growth rates, µB and µS, respectively, and different switching rates a and b. Note that these parameters depend on growth conditions. (B) Measurement and fit to the analytical solution of equations Equations 1 and 2 during exponential growth under activating conditions with initial conditions B(t = 0)=1, S(t = 0)=0, see Materials and methods-Mathematical model. Green and red lines are ScanLag measurements of the SMALL and BIG morphotype fractions, respectively (means ± s.d. of three independent biological replicates). Solid lines are the fit to data using Equations 1 and 2, resulting in a = 0.24 ± 0.13 h−1 and b<<a under activating conditions. These switching rates result in a population dominated by the SMALL morphotype after a few hours. Note that stationary phase caused resetting of the culture to the BIG morphotype. (C) Model (solid line) and experimental measurement (dotted line and markers) of the growth of the total population for the data presented in (B).

    DOI: http://dx.doi.org/10.7554/eLife.19599.007

  • Video 1. Dynamics of self-aggregation observed by time-lapse microscopy in BIG bacteria.

    Bacteria were resuspended from a BIG colony and placed on a wet LB agarose pad for imaging bacteria in suspension. Bacteria divide and remain mostly planktonic.

    DOI: http://dx.doi.org/10.7554/eLife.19599.023

  • Video 2. The dynamics of self-aggregation observed by time-lapse microscopy in SMALL bacteria.

    Bacteria were resuspended from a SMALL colony and placed on a wet LB agarose pad for imaging bacteria in suspension. Bacteria divide and aggregate continuously until they reach stationary phase, which results in the disintegration of the aggregates.

    DOI: http://dx.doi.org/10.7554/eLife.19599.024

  • Video 3. Dynamics of infection by SMALL (green) and BIG (red) bacteria on HeLa cells.

    The SMALL bacteria form microcolonies attached to the HeLa cells, whereas the BIG bacteria remain mostly planktonic (same as Figure 9C).

    DOI: http://dx.doi.org/10.7554/eLife.19599.025

  • Video 4. Dynamics of infection by SMALL (red) and BIG (green) bacteria on HeLa cells.

    The SMALL bacteria form microcolonies attached to the HeLa cells, whereas the BIG bacteria remain mostly planktonic (same as Video 3 but with fluorescent markers opposite tagging).

    DOI: http://dx.doi.org/10.7554/eLife.19599.026