New PET Breaking Enzyme Found in Wastewater Microbes

Microplastics are everywhere, including in wastewater. Because of their small size, they can escape typical water purification processes and re-enter the environment. However, some microbes in wastewater thrive on these plastic particles. One such microbe, Comamonas testosteroni, naturally it degrades sterols like testosterone. While other bacteria like E. coli have been engineered to break down plastic, C. testosteroni does it naturally. However, C. testosteroni naturally chews up polymers, such as those in laundry detergents, and terephthalate, a monomer building block of PET. So, Ludmilla Aristilde and colleagues wanted to see if C. testosteroni could also produce enzymes that degrade the PET polymer.

The team incubated a strain of C. testosteroni with PET films and pellets. While the microbes colonized both, they broke down the rougher surface of the pellets more effectively than the smoother films. To simulate real wastewater conditions, they added acetate, an ion found in wastewater. When acetate was present, the number of bacterial colonies increased considerably. Though C. testosteroni produced some nano-sized PET particles, it also completely degraded the polymer to its monomers — compounds that C. testosteroni and other environmental microbes can use as a source of carbon to grow and develop, or even convert into other useful molecules, according to the team.

The researchers used protein analysis to identify the key enzyme that gives this microbe its plastic-eating abilities. his enzyme, while different from previously known PET-degrading enzymes, had a similar binding pocket for breaking down the plastic.To test its effectiveness, the team inserted the gene for this enzyme into another microbe that doesn't naturally break down PET. The engineered microbe gained the ability to degrade PET, confirming the enzyme's functionality. The researchers say that this work demonstrates C. testosteroni's utility for upcycling PET and PET-derived carbons, which could help reduce plastic pollution in wastewater.

The authors acknowledge funding from the U.S. National Science Foundation, the U.S. Department of Energy, the Office of Energy Efficiency and Renewable Energy, the Advanced Materials and Manufacturing Technologies Office, and the Bioenergy Technologies Office as part of the BOTTLE Consortium.