Biological Modules: Carry

For the carry we thought of a molecule that could transmit a message from one colony to the other.
The communication between cells in Quorum Sensing is a good illustration of the diffusion of a signal between unicellular organisms. We resorted to the system present in Vibrio fischeri using N-Acyl homoserine lactone (AHL).

General principle
AHL is the product of the LuxI gene. On a basic E.calculus colony, this one was placed under the control of promoters belonging to the two AND gates. AHL will be produced when at least one of the AND gates is activated. Then AHL will be transmitted to the following colony by diffusion into LBagar via the Quorum Sensing. It becomes a third input signal (in addition of blue/red lights) that will be taken into consideration for the calculation of the next bit: this is the carry system of our full adder.

Carry module characterization
AHL diffusion into agar medium was characterized thanks to the Chromobacterium violaceum strain. A purple coloration is visible when C. violaceum is in contact with AHL.