Nitogen (N), phosphorus (P) and potassium (K) are three essential macronutrients needed for healthy plant growth. By creating a biological sensor that can quickly provide the status of these macronutrients in the soil, we can provide farmers with the tools to monitor and respond to potential nutrition deficiencies. In previous iGEM projects, nitrate- and phosphate-responsive promoters have been utilized extensively. However, a potassium-responsive promoter was still lacking. Our team submitted the first ever potassium-sensing promoter to the Part Registry, in addition to providing more comprehensive characterization data for the existing phosphate- and nitrate-responsive promoters. Our biological sensors are constructed in E. coli, to detect NPK levels in the surrounding environment and produce a measurable level of reporter protein. To simulate the expression of multiple sensors in a single system, we characterized the effects of a parallel sensor system, in contrast to a single output system.

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The Journey of HKUST-Rice iGEM team

The HKUST-Rice iGEM team is the first transcontinental 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 who 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.