Fig. 4: Growth rate responses differ between repeated fluctuations and single nutrient shifts.

a Average growth rate of single cells over time in four conditions: a single shift in nutrient concentration (occurring at 3 h, after cells had reached steady-state growth in the initial condition), steady C_low, steady C_ave and steady C_high. On the left, a single nutrient upshift (shift from C_low to C_high), and on the right, a single nutrient downshift (from C_high to C_low). After each shift, the growth rate gradually reaches steady-state growth in the post-shift condition. The growth rates in C_low before the upshift and in the steady C_low condition are both within the range of measured steady-state G_low (Supplementary Tables 2 and 7). Data are from one representative experiment. The shaded region marks the portion of single-shift data plotted in (b), which does not include the full progression to steady-state growth after a single up- or downshift. b Growth rate of single cells in fluctuating nutrient conditions stabilizes more rapidly and at a lower value when compared to the growth rate dynamics of cells experiencing a single shift. Data were aligned such that the nutrient shift in all conditions occurs at t = 0. Post-shift data in fluctuating environments are plotted up until the next shift occurs. Shaded error bars denote the standard deviation of the mean among replicate experiments (n = 3–4 for fluctuating conditions; n = 2 for single-shift conditions). c Growth rate is considered stabilized once the slope of the growth signal within a shrinking window reaches zero. Stabilization time is defined as the time between the nutrient shift and the time at which the growth rate is stabilized. d The growth rate of fluctuation-grown cells stabilized at rates lower than steady-state G_high or G_low. Cells experiencing 15 and 60 min fluctuations stabilized at 1.86 ± 0.47 and 1.86 ± 0.13 h⁻¹, respectively, after an upshift and at 0.65 ± 0.22 and 0.60 ± 0.10 h⁻¹ after a downshift. Cells shifted once from steady-state stabilized only upon reaching steady state G_high (2.84 ± 0.08 h⁻¹) after an upshift or G_low (0.96 h⁻¹) when growth rate stabilized after a downshift (only one of two replicates stabilized at G_low after 5 h of post-shift observation). e Cells grown in fluctuations stabilize in growth rate within 3.8 ± 0.0 (T = 15 min) or 3.3 ± 1.4 min (T = 60 min) of each upshift and within 2.2 ± 1.9 (T = 15 min) or 15.0 ± 7.6 min (T = 60 min) of each downshift (n = 3–4). Cells grown in steady environments stabilize hours after a single shift, 116.3 ± 12.4 min in the case of upshifts (n = 2) and at least 297.5 min after a downshift (one of two replicates stabilized after 5 h). f The initial change in growth rate in the minutes following a nutrient shift differed between cells experiencing fluctuations and cells experiencing only a single shift. Over the first 7.5 min after each upshift, cells experiencing fluctuations increased in growth rate relative to their pre-shift growth rate (t = 0) by 138.3 ± 20.6% (15 min) or 158.7 ± 48.4% (60 min), compared to a 12.0 ± 14.0% increase in the single-shift case. Over the 7.5 min after each downshift, cells experiencing fluctuations decreased in growth rate by 57.8 ± 3.7% (15 min) or 80.4 ± 2.6% (60 min), compared to a 90.9 ± 2.5% decrease in growth rate in cells after a single shift. d–f Error bars denote the standard deviation of the mean of n = 3 or 4 biologically independent experimental replicates (none displayed for n < 3). Overlaid data points represent measurements from each of n replicates.