How Bacteria Could Revolutionize Plastic Waste Cleanup

With over 7 billion tonnes of plastic waste generated globally and less than 10% recycled, finding sustainable solutions to plastic pollution is urgent. Millions of tonnes of this waste either accumulate in the environment or are transported across the globe, only to be incinerated or landfilled, resulting in an annual economic loss of $80-120 billion due to the inefficient sorting and processing of plastic packaging waste, as estimated by the UN Environment Programme. However, a breakthrough by researchers at Northwestern University may offer new hope in tackling this mounting challenge.

A team led by Ludmilla Aristilde, associate professor of civil and environmental engineering at Northwestern, has identified how a common bacterium, Comamonas testosteroni, can transform plastic waste into a potential food source. The bacterium, part of the Comamonadaceae family, has been frequently found growing on plastics in urban rivers and wastewater systems. The key to its success lies in a unique sequence of plastic degradation steps: first, the bacterium breaks the plastic into smaller fragments known as nanoplastics. Next, it releases a specialized enzyme to further degrade these fragments into simpler components, which it then consumes as a nutrient source.

“It’s remarkable that a single bacterium can perform this entire process. We pinpointed a key enzyme responsible for breaking down the plastic material, which could be optimized and harnessed to eliminate plastics from the environment,” said Aristilde. The study, recently published in Environmental Science & Technology, opens new possibilities for using bacteria-based engineering solutions to manage plastic waste that contaminates water systems and threatens wildlife.

Investigating the Breakdown of PET Plastics

Aristilde’s research builds on her team’s previous studies, which examined how C. testosteroni metabolizes carbon compounds from plant and plastic degradation. In this new work, the focus was on C. testosteroni’s interaction with polyethylene terephthalate (PET)—a durable plastic used extensively in food packaging and beverage bottles. PET is a major contributor to global plastic pollution, accounting for approximately 12% of total plastic usage and up to 50% of microplastics found in wastewater.

To understand how C. testosteroni interacts with PET, the team conducted a series of laboratory experiments. They cultivated the bacteria on PET films and pellets, using advanced microscopy to track changes in the plastic surface over time. They also analyzed the surrounding water for evidence of nano-sized plastic particles and examined the internal structure of the bacteria to identify the enzymes involved in the degradation process.

A Key Enzyme Unlocked

The findings revealed that when exposed to PET, C. testosteroni expressed a specific enzyme that plays a critical role in breaking down the plastic. Collaborators at Oak Ridge National Laboratory in Tennessee further tested the enzyme’s role by creating bacterial strains lacking the ability to produce it. The results were striking—without this enzyme, the bacteria lost most of their plastic-degrading capabilities. “This suggests that this enzyme is essential for plastic breakdown,” Aristilde explained.

Implications for Wastewater and Environmental Health

The discovery could have significant implications not only for environmental cleanup but also for understanding the behavior of plastics in wastewater systems. Aristilde notes that wastewater is a major reservoir for microplastics and nanoplastics. “Most people assume nanoplastics enter wastewater treatment plants as nanoplastics. But we’ve shown that microbial activity can break down larger plastics into nanoplastics during treatment,” she said. This finding underscores the need to closely monitor how plastics transform during their journey through wastewater systems into rivers and lakes.

By uncovering the mechanism through which C. testosteroni degrades PET, the researchers have provided a foundation for future applications that could harness this bacterium for large-scale plastic cleanup efforts. With further optimization, these bioengineered solutions could be a critical tool in the global fight against plastic pollution.