Team:UNebraska-Lincoln/Composite Part

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Composite Part

The overall goal of our project was to develop an organism capable of reducing excess nitrate in local waterways. However, we don't want our genetically engineered machine to remain in the environment after it has sufficiently reduced nitrate levels. To ensure the safety of our system, we developed this composite biobrick to act as our kill switch. In Jurassic Park, Henry Wu developed a "Lysine Contingency" to ensure the dinosaurs could not survive without sufficient lysine supplemented in their food. Similarly, we designed a "Serine Contingency" kill switch for our bacteria. (Although it is our hope that our kill switch mechanism will function more effectively than the fictional one described in the novel.)

To do this, we complemented an auxotrophic strain of E. coli that is unable to synthesize serine with a plasmid that contains the missing gene, serA. This gene codes for D-3-phosphoglycerate dehydrogenase, an essential enzyme in serine biosynthesis. The promoter we used in this plasmid, yeaR, is normally inhibited and only allows transcription when the nitrate concentration exceeds a certain threshold. Thus, when the nitrate levels have sufficiently declined because the cells have done their job, transcription of serA will be inhibited. Consequently, the cells will not be able to synthesize serine and will no longer be able to survive.

The mechanism of our kill switch is depicted here, where in the presence of nitrate, serine is expressed, and the cell is able to survive. Once it has 'done its job', the nitrate will no longer be present, and so PyeaR and consequently serA will no longer be expressed.

You can view more information and characterization results on the part page: K2086002