Abstract
The Challenge:
Global dependence on plastic is a profound and growing issue. Due to the versatile properties of plastic, such as lightweight, high durability, flexibility, and low production cost, it has become a large part of human life. Between 1950 and 2018, plastic production increased about 180 times. In 2022, the worldwide production of plastic was around 400.3 million tons. As the world becomes increasingly urbanized and the economy and population increases, plastic consumption and waste has been driven to also increase (Pilapitiya & Ratnayake, 2024).
Through the utilization of computational tools and Flux Balance Analysis (FBA), we will optimize the pathways designed to maximize the flux towards BHB production. This will include the use of kinetic models in the prediction and optimization of the enzyme activity based on varying substrate concentrations.
By designing and constructing novel biological parts, we’re aiming to develop an innovative production process that is in line with circular economy principles. This will not only facilitate the conversion of PET plastic waste into high-value products but also offer a sustainable solution to one of the world’s most pressing environmental issues of our time.
In a response to the global challenge of plastic waste, our iGEM project is looking to develop novel biological pathways for the upcycling of polyethylene terephthalate (PET) plastic into beta-hydroxybutyrate (BHB), a high-value product. Our goal is to transform the degradation of PET into its monomeric components possible and further convert those into BHB. By designing and constructing novel biological parts, we aim to establish an innovative production pathway that aligns with circular economy principles. This will not only enable the conversion of PET plastic waste into valuable products but also provide a sustainable solution to one of the largest environmental problems of our time.
Our Solution:
Through the engineering of microorganisms capable of breaking down PET waste in controlled, aqueous environments, our team provides an alternative to existing recycling methods that helps avoid any toxic byproducts and greenhouse gas emissions. By converting PET into high-value products, we open up broader opportunities within the bioremediation field. This will not only enable the conversion of PET plastic waste into valuable products but also provide a more sustainable solution to one of the largest environmental problems of our time.
This was achieved through a series of engineered biological pathways in E.coli and Pseudomonas putida. First, in E. coli, PET is broken down into TPA by a mutated PETase enzyme coded by LCC-ICCG gene with H218y mutation. The TPA is then imported into the cell via a TPA transporter and converted into PCA by a multi-enzyme system including terephthalate dioxygenase (TphA1, A2, A3) and a dehydrogenase (DCDDH). This PCA can be funneled into central metabolism through the pca gene cluster (PcaGH, B, C, D, IJ, F), which cleaves the aromatic ring and ultimately produces Acetyl-CoA. This Acetyl-CoA serves as the building block for PHB, a biodegradable plastic, through the action of the phaCAB operon (PhaA, PhaB, PhaC). Since E.coli can’t metabolize TPA naturally, we also engineered a parallel, more direct route in P. putida, where TPA can be converted directly into PHB using the same phaCAB operon. Finally, to create a valuable supplement, we engineered a pathway where PHB is hydrolyzed into beta-hydroxybutyrate (BHB) by PHB depolymerase enzyme (PHAZ_TALFU). Our experimental data has successfully validated key parts of this pipeline, confirming the functionality of our PETase, TPA transporter, and PHB depolymerase, proving the feasibility of transforming plastic waste into sustainable materials and products.
One of the high-value products, BHB, also addresses the problem with current BHB supplements. The biological synthesis of BHB, as opposed to current chemical methods, offers superior enantiomeric control, producing only the d-isomer of BHB and minimizing the risk of contamination. It is identical to the endogenous D-3HB, and has significantly reduced heavy metal content (Yao et al. 2021)
Project inspiration:
Plastic waste is currently one of the most pressing environmental issues in the world today, along with its influence towards global warming. 2000 garbage trucks full of plastic are emitted into natural ecosystems every day (UNEP, 2025). The economic value of plastic itself is drastically decreased after use, leading to large economic losses. Therefore, our iGEM project was aimed to develop an innovative biological pathway to upcycle polyethylene terephthalate (PET) plastic into beta-hydroxybutyrate (BHB). We want to enable the degradation of PET into monomeric constituents and further convert those into BHB.
Future Visions
We envision a future where our engineered construct can be used to decrease plastic waste and help upcycle PET, where a circular economy is achieved. By using engineered bacteria to break down plastic waste, we can progress from landfill waste and pollution, and create a more sustainable future.