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The main objective of our team’s project is to create a bi-directional logical construct using quorum sensing E. coli in a microfluidic chip. We intend to design two different strains of genetically engineered E. coli both capable of sending and receiving different signaling molecules. By patterning the two types of cells near one another in a microfluidic channel we should be able to have molecules secreted by one influence the other and we should be able to control the directionality of communication by changing the direction of flow in the channel. This system is a bacterial analog of a Zener diode, which allows electrical current to only flow in one direction above a voltage threshold and only in the opposite direction below a different voltage threshold.

Our first E. coli strain carries both LuxI gene capable of producing acyl homoserine lactone (AHL) and LuxAB gene capable of producing luciferase. The second E. coli strain carries both LuxR operon attached with a GFP reporter gene and Lux CDE luciferin production gene. The two strains of E. coli are then placed next to each other inside the microfluidic channel trapped in a hydrogel matrix. When solution is pumped inside the microfluidic channel travelling from the first patch of E. coli to the second, AHL secreted from the first patch is carried through to the second patch. AHL will then bind with the LuxR protein in the second patch, activating the LuxpR promoter and triggering the production of green fluorescent protein. Meanwhile, the luciferin produced by the second patch of E. coli will only travel downstream further away from the first patch without triggering any response from the first patch.

Alternatively, if the solution is pumped inside the microfluidic channel travelling from the second patch to the first patch of E. coli, then Luciferin produced from the second patch will be received by the first patch. Under the enzymatic activity of luciferase produced by the first patch, luciferin will undergo a chemiluminescent reaction and generate blue light.

Our device will be capable of controlling the direction of communication based on the direction of flow in a channel. The orthogonal visual responses, one fluorescent and one luminescent, should be clear indicators of which way communication took place. This new construct will be a novel member of the growing toolkit available to perform logic operations with living systems.

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