To combat the alarming rise in plastic pollution worldwide, researchers have developed a synthetic microorganism ecosystem that works collectively to upcycle plastics into desired chemicals. Instead of trying to synthesize a single organism that can perform all of the upcycling steps, the researchers utilized two strains of bacteria to efficiently degrade one of the most common plastics, polyethylene terephthalate (PET), into nontoxic, environment-friendly, and biodegradable polymers.

The research article, “Engineering microbial division of labor for plastic upcycling,” was published in Nature Communications by University of Illinois Urbana-Champaign professor of bioengineering Ting Lu, PhD, Massachusetts Institute of Technology (MIT) professor of medical engineering & science James J. Collins, PhD, and colleagues.

Collins was featured as one of Clarivate’s 2023 Citation Laureates, researchers whose work is deemed to be of Nobel stature, for his pioneering work with Michael Elowitz and Stanislas Leibler on synthetic gene circuits, which launched the field of synthetic biology.

Two is better than one

Bioconversion using microorganisms is quickly becoming a viable alternative to traditional polymer upcycling methods due to its potential to streamline production processes and combine waste degradation and product generation. For example, various microbial isolates have been discovered and used to break down and assimilate PET. There are also engineered bacterial and fungal strains that can speed up PET hydrolysis and turn plastic trash into useful chemicals and products.

Despite these promising advances, the complexity of polymer upcycling presents several challenges for current biotransformation approaches that focus on monocultures.

The paper’s co-lead authors, Teng Bao, Yuanchao Qian, and Yongping Xin, modified two strains of the soil bacterium Pseudomonas putida to degrade PET. Each strain was in charge of processing only one of the two compounds produced as a byproduct of chemical plastic breakdown: terephthalic acid or ethylene glycol. These strains improved productivity when used in tandem instead of using a single strain for both products. The bacteria then upcycled the plastic into the biodegradable polymer medium-chain length polyhydroxyalkanoates (mcl-PHA) and the polyurethane and adipic acid precursor cis-cis muconate (MA). Polyurethane is used in insulators, foams, coatings, and adhesives, and nylon is made from adipic acid.

This designer upcycling consortium can be used to make more chemicals besides mcl-PHA and muconate. They can do this by adding new biosynthetic pathways and connecting them to the main metabolic nodes in TPA and EG catabolism by using their modular structure. Additionally, while the study was limited to PET upcycling, the underlying concept and strategies are potentially applicable to the treatment of other types of plastics, thereby offering insight into developing a sustainable bioeconomy.

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