Fig. 4.

Growth environment, rather than growth time, determines Tar/Tsr ratio through growth rate-dependent chemoreceptor expression. (a) Schematic of the experimental protocol to assess the effect of growth time on the chemoreceptor ratio distributions. Cells from the same saturated culture were diluted to three different concentrations in fresh rich media and all cultures were harvested at the same optical density (OD = 0.45). (b) Histograms of the Tar/Tsr chemoreceptor ratio, measured via fluorescence microscopy, for the three different dilutions in a single experiment. The receptor ratio distribution is independent of the dilution factor. Error bars indicate 95% confidence intervals obtained through bootstrap resampling. Inset: Growth time as a function of dilution. (c) Schematic of experimental protocol to assess the effect of the growth environment on chemoreceptor ratio distributions. Cells were grown in rich media to OD = 0.30 and OD = 0.80, after which they were separated from their supernatant. The Tar/Tsr chemoreceptor ratio was measured via fluorescence microscopy in both the harvested cells and in cells growing inside a microfluidic chemostat at steady state, where they were exposed to the collected supernatant. (d)Histograms of the Tar/Tsr chemoreceptor ratio for harvested cells (solid lines) and for cells growing inside the chemostat while exposed to supernatant (points). Solid lines and points represent the histograms of all measured Tar/Tsr ratios from a single experiment. Shaded areas and error bars indicate 95% confidence intervals obtained through bootstrap resampling. Inset: growth rate of the cells in the batch culture at OD = 0.30 and OD = 0.80, assessed using a plate reader. Bar plots are the means of 40 technical replicates.