Biological Modules

Full Adder

With a logic diagram, a full adder can be illustrated with 5 logic gates (2 XOR, 2 AND and 1 OR) A and B represent the two operands and Cin and Cout the carrie.

In our biological system, this diagram represents the input part.

A general inducer has been used to start the counting in order to differentiate the off state where there is no counting and the on state adding 0+0. TetR gene is put after a constitutive promoter and every input genes (Carry system genes, Blue and Red light receptor genes) are after a PtetR promoter that is repressed in presence of TetR. When we want the counting to be started, we add ATC (Anhydrotetracycline) that bind TetR and let the transcription of the input genes.
When there is a carry diffusing from the previous colony, the AHL will bind the LuxR protein produce by luxR gene. This can then activate the Plux promoter with induced the production of PhiC31 recombinase.
In absence of blue (480 nm) or red (660 nm) light, both light receptor systems will be activated and induce the production of respectively Bxb1 and tp901.1.

And this diagram combines the four logic gates.

The production of TP 901.1 and Bxb1 are the inputs (A and B) and PhiC31 is produced after the detection of a carry.
There is no OR gate but it is replaced by the two luxI gene. If there is one or the other produced, it replace a OR gate.