IGEM:IMPERIAL/2007/Projects/pH Buffering Machine

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pH Buffering Machine: Introduction

The E.coli cad operon consists of the genes coding for CadC, CadB and CadA. CadC is an activator of the promoter pCad. However, pCad is only activated at low pH. We plan to make use of this pH-inducible property of pCad to build a pH buffering machine.

  • At low pH, pCad is activated. By placing the gene coding for urease downstream of pCad, urease is expressed at low pH. Urease breaks down urea into carbon dioxide and ammonia. This raises the pH.
  • At high pH, pCad is inactivated. By placing an inverter device downstream of pCad, followed by the gene coding for lactate dehydrogenase, lactate dehydrogenase is expressed at high pH. Lactate dehydrogenase converts pyruvate to lactate. This lowers the pH.

In this way, our genetically engineered pH buffering machine maintains the pH at around pH 7.