The Issue

Figure 1. People face pathogenic threats in daily life (Picture by Tsinghua iGEM team 2013)

Life-threatening pathogenic infections cause thousands of deaths every week all around the world. An effective and efficient identification of the infectious pathogens would facilitate the clinical treatment of these diseases. Nevertheless, current methods for identifying pathogens have many drawbacks including the long period required for test, the high cost resulted from multiple complex reactions and the lack of portable facilities. Clinical diagnosis of infectious pathogens would benefit significantly from specific and sensitive pathogen identification methods better than existing ones including pathogen culture, immunoassays and polymerase chain reaction (PCR) testing.

Opportunities for synthetic biology in mobile health

Inspired by quorum sensing, a classical iGEM system under reconstruction and utilization, we designed a novel pathogen detection and identification system. The detecting system is made in the form of test paper, which can be carried by hand and used conveniently. More importantly, it’s much safer than the traditional iGEM detectors, as the system we used is S. cerevisiae (budding yeast). To accomplish the detection, people who suspect themselves to be infected only need to add a few drops of water as well as their pathogen-rich biological samples like snot or tears onto the test paper. Different color change of the test paper indicates different pathogen-specific infection. As some infections are caused by multiple pathogens, we constructed a switch-box composed of different sensors and different reporters in order to detect multiple pathogens at the same time. This system increases the speed and portability of pathogen identification method, decreases the cost for producing practical facilities, and enables specific identification of distinct infectious pathogens. The challenge is addressed by implementing the genetically modified S. cerevisiae (budding yeast) for testing signal molecules from pathogens. The system is supposed to be effective, reliable, safe and cost-effective.

Figure 2. Target health problems with synthetic biology (Picture by Tsinghua iGEM team 2013)

Idea of our project

The project introduces the use of genetically engineered cells in a pathogen identification system. By virtue of the switchable haploid/diploid form of yeast, two kinds of haploid budding yeast have been constructed, one for sensing the signal molecules from pathogens and the other reporting the identification of pathogens, referred to as sensing module and reporting module, respectively. The sensing module and reporting module are combined together by mating between the two differently engineered yeasts, and the signals from pathogens are sensed and reported by change in the color of the yeast colony. N-Acyl Homoserine Lactone (AHL) is the signal to be tested by the sensing module. It is the molecule for quorum sensing in Gram-negative bacteria with specificity for each different species of pathogens. Tetracycline-controlled transcriptional activation system (Tet-off system) is introduced to transmit signals from the sensing module to the reporting module. Considering the specificity and sensitivity of this pathogen identification sensor, this technology could be useful for clinical test, medical diagnostics, water quality monitoring, and other potential applications.

Figure 1. Principles of the project
(Picture by Tsinghua iGEM team 2013)

Achievements

• We accomplished the communication between eukaryotic cells and prokaryotic cells for the first time via introducing the genetically modified quorum sensing system from Gram-negative bacteria (LuxR-AHL controlled transcriptional activation system) to S. cerevisiae (budding yeast) by designing eukaryotic-prokaryotic mosaic transcriptional activator and promoter, referred as LuxR-tVP16 and Plux-mCyc respectively, which provided more possibilities for future iGEM projects.
• We designed and completed the switching system by mating different reporting modules with the sensing module.
• We constructed a mathematical model to demonstrate the sensitivity and robustness of this system combining modified quorum sensing and tetracycline controlled transcriptional activation systems.
• We provided several novel BioBricks to the Registry.
• We improved the existing BioBricks.
• We introduced the project and synthetic biology to the society by activities including making videos.