Figure 5

Conditional perturbation based on the number of cells. (A) Sketch of the protocol, showing that different positions have a different conditional statement (\(\langle {\text{IF}} \rangle\)) on the number of cells to trigger the switch from glucose to sucrose independently of each other. (B) Sucrose conversion by yeast. The Suc2p invertase produced by cells is secreted extracellularly and can degrade extracellular sucrose into diffusible hexose. (C) Following a shift from glucose to sucrose, cells need some time to convert sucrose to glucose and restart division. We show here that this time depends on the initial cell density (the higher the number of cells, the shorter the lag phase). The duration of the lag phase was estimated as the time it took the population to reach 130% of its initial size after the switch from glucose to sucrose. Error bars represent ± one standard deviation over three biological replicates (two replicates for the *). (D) Temporal evolution of the number of cells for different initial densities: 100 (1), 500 (2) and 2000 (3) cells (grey arrows). (E) Population growth shifted temporally to the switch time (i.e., switch = t₀), demonstrating that the lag time increases as the initial cell density decreases. (F) Cell counting is achieved by real-time segmentation, shown here as an overlay of the brightfield image with single cell masks (in blue) at the time of the valve switch.