Team:IIT Delhi/Model

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Our lab work during this summer was carried out based on the idea of making a comprehensive bacterial pH sensor. For this purpose we used three widely studied promoters, one was acid inducible (asr) and another was inducible in alkaline condition (ATP2) and third was repressible promoter (Ptet). So our gene network is created in such a way that it works pretty well in a range of pH which varies from acidic pH to alkaline pH.
SO here, we created a short video giving an incite into the working of the model of our system.







There can be three possible cases in which our bacterial pH sensor will work which are given below-

Case-1
At neutral pH (7.0) our system only synthesizes the Green fluorescent protein (GFP) thus our culture would show green color.

Case-2
At acidic pH (<7.0) asr promoter gets induced accordingly and produces Red fluorescent protein (RFP) along with tetR. Because of RFP production this would generate red color in the system and along with the existing GFP this gives a gradient of color. Simultaneously tetR carries out repression of Ptet promoter. Due to this GFP transcription decreases and the green color reduces and giving rise to a dominant red color.
Similarly in the reverse process as acidity reduces, RFP transcription would reduce. Also inhibition by tetR would be reduced, this would lead to increased production of GFP and green color would be dominant.

Case-3
At alkaline pH (>7.0) the ATP2 promoter would get induced and produces lac Z which gives rise to blue color. Simultaneously, tet R is formed which suppresses Ptet promoter activity And this results in reduction of GFP transcription so the intensity of blue color in the culture increases.
Likewise, in the reverse process as OH negative concentration decreases Lac Z transcription reduces and this results in reduction of blue color. Also tetR production reduces which decreases the repression of Ptet promoter and as you approach neutral pH this results in increased production GFP, and green color intensity increases.