Figure 1.
(a) Bacteria residing in a spherical biofilm micro-colony attached to a surface; (b) example of a regulatory motif in a single cell. The signal molecules S are synthesized under the control of the promoter PS. The signal molecules diffuse freely in/out of the cell and between cells in the colony. The cell produces a regulator, R, which dimerizes and binds signal molecules, typically from other cells, to form the activated regulator, R2S2. The concentration of the activated regulator now constitutes a proxy of the “size” of the population and can be used to control size-dependent gene regulation. The activated regulator can bind to the promoter to increase the signal molecule production. When this happens, the positive feedback ignites the whole colony, allowing for the concentration of signal molecules and activated regulators to increase dramatically. The figure is adapted from figures in [11]—published by The Royal Society of Chemistry.