Nitrogen (N), phosphorus (P) and potassium (K) are three plant macronutrients that are essential for healthy plant growth, and deficiencies in any of these can lead to plant diseases. By creating a biological sensor that can quickly provide the status of these macronutrients in the soil, we can provide plant owners the tools to monitor and respond to potential deficiencies.

In previous iGEM competitions, nitrate and phosphate responsive promoters have been explored extensively. However, a potassium responsive promoter is still lacking. In light of this deficiency, our team constructed a biological sensor in E. coli, which can detect NPK levels in the surrounding environment and give responses in the form of colors. In addition, we characterized the effects of a parallel sensor system, in contrast to a single output system, in order to anticipate the expression of multiple outputs in a single system.

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The Journey of HKUST-Rice iGEM team

We are the HKUST-Rice iGEM team. Our team is the first cross continental team in iGEM, comprising of 31 student members- 18 from the Hong Kong University of Science and Technology and 13 from Rice University. The benefit of forming a large joint team is that we have members coming from different disciplines which contribute different perspectives to the project. This has enabled us to tackle a broad subject matter effectively.

Taking the native metabolic pathway found in E. coli, we have designed a potassium ion (K⁺) regulated construct and a nitrate-(NO₃^-) regulated construct that could potentially report the K⁺ and NO₃^- level in soil. Since previous iGEM teams have also worked on nitrate-regulated promoters and phosphate-regulated promoters, our team utilized these promoters and further characterized them in order to provide more information on these promoters.

In addition, we characterized the effects of a parallel sensor system, in contrast to a single output system, in order to predict the expression of multiple outputs in a single system.

When it comes to the real application method of our biosensors, our team considered two factors- biological safety and feasibility. Biological safety is our priority, especially since the practical application of our project is related to the agricultural business. In our plan of applying the biosensor, we chose to deliver the biosensor in a cell-free system, which has no capability to sustain itself in the wild. However, after factoring in the feasibility, we think that delivering our biosensor in common soil bacteria will be more practical. Hence we perform proof-of-concept experiments to demonstrate our idea.

Besides lab work, we also engaged the community- introducing synthetic biology to the younger community by debating and interacting with and gathering the community's perception regarding biosensors and genetic engineering technology. Through engagement with the community, we gained valuable feedback and comments which we then used to improve our design.