Pattern Sensing

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Science  29 Nov 2013:
Vol. 342, Issue 6162, pp. 1020-1021
DOI: 10.1126/science.342.6162.1020-d

More than 60 years ago, Alan Turing described how self-regulated biological patterns could arise in his reaction-diffusion model: An activator and a repressor interact and diffuse at different rates. Payne et al. developed a synthetic system to implement this model by engineering two circuits into bacteria: (i) a mutant T7 RNA polymerase that activates its own promoter plus cyan fluorescent protein (CFP), and (ii) an inhibitory circuit containing the gene for lysozyme, which inhibits T7 RNA polymerase and was linked to the fluorescent mCherry protein. The T7 RNA polymerase induced expression of LuxI, which is involved in the synthesis of acylhomoserine lactone (AHL). High concentrations of AHL induced LuxR expression, which in turn induced the expression of T7 lysozyme, resulting in the inhibition of the T7 RNA promoter. Microcolonies, launched from individual cells, displayed a CFP core and an mCherry ring. Modeling studies incorporating the metabolic burdens imposed by the circuits suggested that cell growth and gene expression were linked so that the activation signal acted as a timing mechanism that enabled the colony to sense its environment. The larger the environment, the longer it took for the activating signal to reach a critical concentration that triggered pattern formation and the larger the ring.

Mol. Syst. Biol. 9, 697 (2013).

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