Figure 2.

Single-cell oscillating behaviour. (a) The GRN of a single cell in experiments presented in Danino et al. [2]. Th luxI gene encodes for the LuxI enzyme (LI), which produces the molecule acyl homoserine lactone (A). AHL combines with the constitutively expressed LuxR that is modelled as a constant, to form a complex, L:A, that can activate the promoter li-P. This drives the expression of all three genes: gfp, aiiA and luxI. AHL is removed from the system by enzymatic degradation catalysed by the aA enzyme (aA). AHL can also freely diffuse through the cell membrane. Positive and negative feedbacks steps within this network are indicated with a red plus/minus sign, respectively. (b) In the oscillating regime, oscillations are characterized by a period of approximately 410–420 min. The inset shows a magnification of the area that is highlighted with a bold line on the x-axis to illustrate the oscillations of the lower concentration components. (c) A projection of trajectories in three-dimensional space defined by the concentrations of aA, LA and Ã. Trajectories with sufficient external AHL concentration tend to the limit cycle. The gradient key illustrates the value of the increasing concentration of external AHL ([Ã]) in initial conditions of model simulations.