Team:KEYSTONE/Description
Plastics are considered a powerful invention. It has diffused into most aspects of the human life. However, annually, 800,000 tons of plastic enters the ocean, contributing their own effort to the existing 10,000s to 100,000s tons of plastic that are currently in our oceans [1]. Narrowing the focus to PET plastic, in the U.S., less than 30% of the PET plastic containers that enters the market will be recycled for other use, while others remains in nature after disposal [2].
In the beginning of our team’s iGEM experience, we were reminded of our school’s plastic-free policy and decided to contribute our efforts to solving problems of plastic pollution.
Inspired by Beijing’s new trash sorting policies when we started the project, we came up with the idea of trash can: a trash can that can degrade plastic right after it has been thrown away. We also researched possible fragrance because of our universal agreement on the unpleasantness of some trash cans’ odor.
Multiple human practices have helped carve out the final shape of our project. Interview of Xue Yang from Plastic Reuse and Recycle Association, Sierra and Rosa from Biosphere Foundation in Bali, as well as an original survey regarding trash at tourist sites.
Our interview of Xue Yang gave our team a clear picture on the current plastic recycling and plastic degradation industry. We became aware that our product potentially lack demand in cities were PET plastic remanufacture systems are already established, but we also realized that our original goal fits more with natural tourist sites, for example, Bali, where the plastic products are brought by tourists, where construction of large recycling factories lack feasibility, where natural system is fragile. Our interview with Sierra from Biosphere Foundation confirmed the need for small, plastic degrading units like the trash can that our team was envisioning.
With our focus narrowed to plastic degrading trash can at tourist sites, we moved on to confirming the actual demand of the product by surveying our target audiences. Our survey reached more than 200 people. Based on the results, more than 82% of all survey respondents are disturbed by the littering at tourists’ sites and 61% of them think that plastic pollution is very serious at scenic areas. However, 84% are currently are highly aware of not harming the environment while traveling and all respondents are cautious about littering at tourist sites through different measures. This confirms the need for our product as current precautions are no longer working. The fragrance will also potentially improve their tourist experience.
Finally, our team agreed to develop a trash can that can degrade plastic and produce a fragrance that would improve the “approachability” of the trash cans and the tourists’ experiences. We were also hoping to incorporate elements that will educate the public about the importance of plastic degradation and environmental protection on the trash cans.
The accomplishment of the our iGEM project this year has two main sectors-- the experiments, which includes the fragrance and plastic degradation, and the hardware.
The plastic degradation experiment mainly uses the leaf-compost cutinase enzyme. According to the article published on Nature, the LCC enzyme is currently the most effective enzyme that degrades PET plastic. This result came from a comparison with other enzymes including PETase and BTA; the specific mutation that we are using, which is LCC-ICCG, is the most effective and thermostable strain of this enzyme [3]. LCC will degrade PET polymers into its substrates TPA and EG. The aim of our experiments was to insert these genes into the E. coli and optimize conditions for translation of the LCC enzyme as well as the conditions for degradation of the PET plastic. The final optimal condition will further inform us about the setting of the decomposer section of our trash can.
To improve tourists’ experiences, we are also using E. coli to produce fragrance, reducing the smell from trash cans at tourist sites. This function is accomplished with the enzyme bLIS, which produces Linalool, a common fragrance in the detergents, perfume, and even some beverages. There are varies types of Linalool synthase, and the currently most effective one is bLIS, the linalool synthase from Streptomyces clavuligerus [4]. For the reaction to produce Linalool, a main substrate is GPP, which would be produced by the geranyl pyrophosphate synthase. A plasmid is constructed through PCR for this purpose, containing the gene for geranyl pyrophosphate synthase and linalool synthase. It has been inserted into the E. coli to help synthesize linalool through the translation of the respective enzymes. The GPPS will synthesize GPP, and the GPP will be used by bLIS to produce Linalool, our target fragrance.
The hardware product is the final step in achieving our team’s vision of a plastic degrading trash system. The mechanical trash can is comprised of three parts the shredder, the power source, and the decomposer. The shredder is powered by a motor to shred the PET plastic into smaller pieces to ensure the PET plastics are efficiently degraded. The decomposer contains the E. coli, and the PET plastic pieces will be submerged in the fluid inside the decomposer for degradation. This could also be combined with the enzymes of other teams to become a composite trash can that can degrade more than one type of plastic. In the real-world scenario, there would be replacements of E. coli put in manually. Even though this does not completely replace the need of human labor for trash collection and recycling, it does extent the replacement period of plastic litter facility, easing the pressure on the entire trash labor.
[1] Ritchie, H. & Roser, M. (Sep. 2018). Plastic pollution. Retrieved from https://ourworldindata.org/plastic-pollution. [2] The Association of Plastic Recyclers. (Nov. 15, 2018). Report on postconsumer PET container recycling activity in 2017. https://www.epa.gov/facts-and-figures-about-materials-waste-and-recycling/plastics-material-specific-data. [3] Tournier, V., Topham, C.M., Gilles, A. et al (2020). An engineered PET depolymerase to break down and recycle plastic bottles. Nature 580, 216–219. https://doi.org/10.1038/s41586-020-2149-4. [4] Xun, W., Jing, W., Jiaming, C. et al (2019). Efficient Biosynthesis of R-(-)-linalool through Adjusting Expression Strategy and Increasing GPP Supply in Escherichia coli. https://doi.org/10.21203/rs.2.18761/v1.
