Figure 4

Spatial organization of cellular populations via engineered communication circuits. (A) A genetic circuit that generates periodic stripes in space. The LuxI/LuxR QS system is coupled to cellular motility via the transcriptional repressor gene cI, which is induced by AHL via the promoter P_luxI and inhibits the expression of cheZ, one of the essential genes in bacteria motility. At a low cell density, AHL concentration remains low and no CI is produced, leading to a constant production of CheZ and hence a high cell motility. In a high cell density, sufficient accumulation of the AHL induces CI production which in turn suppresses cheZ expression, resulting in a deficiency in cell motility. The density-dependent motility of the population generates periodic stripe patterns in an expanding cell population. (B) A multi-module, communication-based synthetic circuit that allows accurate edge detection. Three functional modules are involved, including a light sensor, a cell communication module, and an X AND (NOT Y) gate. Upon exposure to red light, the light-sensing protein Cph8 induces the expression of cI and luxI: CI represses the expression of lacZ in the same cell regardless of AHL concentration while LuxI triggers the production of AHL that can diffuse to neighboring cells in the dark region to induce the production of LacZ. On the other hand, cells far from the light cannot produce LacZ because no AHL is available to trigger the transcription. As a result, only the cells near the edge of the light-exposed area actively express lacZ, which results in a dark pigment due to the enzymatic cleavage of a substrate in the plate by LacZ.