In today's world, as we face significant challenges of environmental pollution, especially plastic waste, discoveries about the ability of certain bacteria to degrade plastic represent a major advancement. A group of bacteria known as Comamonadacae has come to the forefront of researchers' attention due to its ability to thrive on plastics found in urban rivers and wastewater systems. Until recently, it remained unclear how these bacteria actually function and what impact they have on plastic degradation.

A research team from Northwestern University discovered the mechanisms by which Comamonas bacteria degrade plastic for nourishment. In the first step, the bacteria shred the plastic into small pieces, known as nanoplastics, and then secrete a specialized enzyme that further breaks down that plastic. This process concludes when the bacteria utilize a ring of carbon atoms from the plastic as a food source. According to Ludmille Aristilde, who led the study published in the journal Environmental Science & Technology, this discovery represents the first systematic depiction of how wastewater bacteria can take in plastic material, degrade it, break it down, and use it as a source of carbon.

This knowledge opens doors to new possibilities for developing bacteria-based solutions that could help clean up difficult-to-remove plastic waste, which not only pollutes water but also harms wildlife. Understanding these mechanisms will enable the development of bioengineering solutions that could significantly impact environmental remediation.

Research team

Professor Ludmilla Aristilde specializes in the dynamics of organic matter in the environment and works at the McCormick School of Engineering. She is also a member of several institutions, including the Center for Synthetic Biology and the International Institute for Nanotechnology. Co-authors of the study include Rebecca Wilkes, a former doctoral student in Aristilde's lab, and Nanqing Zhou, a current postdoctoral researcher. This study is also the result of collaboration with several former and current students who worked in Aristilde's team.

Plastic pollution problem

This new study is based on previous research that uncovered the mechanisms allowing Comamonas testosteroni to metabolize simple carbohydrates generated from the degradation of plants and plastics. C. testosteroni thrives on poly(ethylene terephthalate) (PET), a type of plastic commonly used in food packaging and beverage bottles. PET is known for its resistance to degradation, making it a significant factor in plastic pollution.

According to Aristilde, PET plastic accounts for about 12% of the total global plastic consumption and is responsible for up to 50% of microplastics found in wastewater. Therefore, researching these bacteria is of utmost importance for understanding and addressing the problem of plastic pollution.

Natural ability to degrade plastic

To better understand the interaction of C. testosteroni with plastic, Aristilde and her team applied various theoretical and experimental approaches. They first cultivated bacteria on PET films and pellets, observing changes on the surface of the plastic material over time. Additionally, they analyzed water around the bacteria searching for evidence of degraded plastic in smaller nano sizes. The researchers also studied the interior of the bacteria to identify the tools they use to degrade PET.

In the presence of bacteria, microplastics break down into tiny nanoparticles, and researchers discovered that this bacterium possesses a natural ability to degrade plastic all the way down to monomers, the small building blocks that combine into polymers. These small components represent a source of bioavailable carbon that bacteria can utilize for their own growth and development.

Key enzyme

Aristilde was also interested in exploring how C. testosteroni degrades plastic. Using omics techniques, which allow for measuring all enzymes within a cell, her team identified a specific enzyme that is activated when the bacterium comes into contact with PET plastic. In collaboration with Oak Ridge National Laboratory in Tennessee, the researchers developed bacterial strains lacking the ability to express this enzyme. Surprisingly, without this enzyme, the bacteria's ability to degrade plastic was significantly reduced.

How plastic changes in water

Besides being potentially used for ecological solutions, Aristilde emphasizes the importance of understanding the changes plastic undergoes in wastewater. Wastewater represents a large reservoir of microplastics and nanoplastics, and most people think these particles enter treatment systems in their final form. However, research shows that nanoplastics can form during the wastewater treatment process through microbiological activity.

This knowledge can help better understand the behavior of plastic as it moves from wastewater to rivers and lakes. It is crucial to monitor how plastic develops in these systems to develop strategies for its removal and reduce its impact on the environment.

Source: Northwestern University