Figure 5.

(a) Stationary probabilities of cell sizes p_n (top, 3297 single cell data points) and cell sizes at birth ${\pi }_n^{⁎}$ (bottom, 488 single cell data points) binned as a function of the state n (l₀ units). The lines correspond to the unbinned, continuous, distributions ρ(l) (top) and ρ(l_b) (bottom). The clustering process defines cell classes depending on the units l₀ contained and allows to compare theoretical predictions and experimental results. By fitting simultaneously the experimental probabilities to the theoretical values (inset shows error minimization as a function of α) we estimated the value of the division efficiency, α = 0.87, when the division pattern considered was all septa to be equiprobable (binomial pattern of division): black circles. Alternative division patterns produce similar results (Fig. S7). (b) Fraction of division events as a function of the ratio, r, between mother and daughter cell sizes as obtained experimentally. The insets show the results of numerical simulations for different division patterns using the value of α as measured in experiments: red, green, blue, and purple stand for binomial, uniform, inverse binomial, and division by the middle respectively. The black triangles point out 1/4 and 3/4 division fractions, barely visible, that reveal the existence of cell sizes up to 4 unit lengths. All tested division patterns but the division by the middle show the 1/4 and 3/4 division ratios. (c) Size increment as a function of the length at birth (both in units of l₀). Points stand for single cell data (252). Grey points (216) account for cells born from symmetric divisions. Green points (36, including one outlier at m = 4 not shown in the figure) indicate cells born from asymmetric divisions (~15% of the division events). Open red circles stand for binned experimental values, open black circles for numerical simulations using the values of l₀ and α as experimentally measured. The black line corresponds to the theoretical estimate, Eq. (10) using N = 20 and α = 0.87. The red line corresponds to the fitting of the experimental binned points to the theoretical estimate 1/α: α = 1.0 ± 0.1. The error bars stand for the standard deviation. (d) Snapshots showing examples of asymmetric division events. Time runs from left to right. 5 μm scale bar in all cases. The outlined cells on the left divide and generate two cells satisfying 1/4–3/4 (top) and 1/3–2/3 (bottom) size relations. The red arrows indicate the location of the septa.