As humanity becomes ever more aware of the scope and severity of the climate crisis it faces, plastic pollution has in many ways become the face of the enormous environmental impact we have inflicted upon our world. From city streets down to the deepest abyss of the oceans, we have left our mark in the form of micro- and macroplastic litter (Chiba et al., 2018). With staggering speed, global plastic production has increased from a humble 2 million tonnes in 1950 up to 438 million tonnes in 2017 and is estimated to reach approximately 1100 million tonnes by 2050. Meanwhile, recycling rates have struggled to keep up, with only about 20% of plastic waste being recycled in 2017, leading to an exceptional amount of plastic waste that is simply discarded (Geyer, R. 2020).

The challenge of plastic recycling is multi-faceted, both from a technological perspective and socio economical. As outlined in IPCC’s 2022 report, both lack of technologies and/or unfavorable economics in recycling remain a hindrance, and as such improving the technologies and policies surrounding plastic recycling is a priority goal for reducing humanity’s environmental impact. Some of plastic’s greatest strengths, its versatility and its resistance to erosion are also one of its greatest drawbacks when it comes to recycling it. The great variety of different plastics and the varying use of additives in plastic means that recycling it into a pure product is a significant challenge and hence recycling of plastics rarely yields a product that is as valuable as the original virgin plastics, undermining the economic grounds for the recycling operation (Shen & Worrell, 2014). Advancements in research surrounding plastic degrading enzymes (Austin et al., 2018) the past years and their use in degradation and consequent upcycling into higher-value chemicals (Sadler & Wallace, 2021) provide an exciting and interesting way of combatting plastic pollution. Not only does the use of biologically derived enzymes provide means of environmentally friendly chemical degradation but coupling the process with enzymes that can convert plastic degradation products into more valuable chemicals has the potential to also make the entire process far more economically feasible. Inspired by this research and motivated by the scale of the plastic problem, we decided to devote our focus this year to plastic degradation and upcycling using biocatalysts!



For our project we decided to focus on degradation of polyethylene terephthalate (PET) plastics since it has the largest number of characterized enzymes (40) that can act on it (Bucholz et al. 2022), and its degradation is arguably the best studied of all the synthetic polymers. Our overarching goal was to build upon previous work surrounding plastic degradation, membrane transport and bacterial upcycling to develop an E. coli strain whole cell catalyst system with a fully integrated metabolic pathway that could both degrade PET plastics and further turn them into the chemical protocatechuic acid (PCA). We chose to aim for an end product of PCA, not only because of realistic limitations of how many metabolic steps we could engineer and integrate over the summer working period, but also since it is a molecule of considerable interest in its own right. PCA has been researched for it’s hypothesized medicinal use as (find original reference here). Furthermore, PCA is a chemical intermediate for a variety of interesting and economically relevant chemicals such as gallic acid, pyrogallol, muconic acid and vanillic acid. These chemicals in turn are then used in the production of perfumes, flavors, pharmaceuticals, sanitizers, and polyurethanes (Kimet al., 2019). We thus concluded that integrating a metabolic pathway up to the production of PCA would be an excellent starting point to prove and develop a single cell biocatalyst system that also offered the possibilities for future teams to build upon. In this way, we hoped to contribute towards solving one aspect of the problem of plastic pollution using the tools of synthetic biology at our disposal.