Researchers at Northwestern University have made a significant discovery regarding the breakdown of plastic by a common family of environmental bacteria known as Comamonadacae. These bacteria, often found in urban rivers and wastewater systems, have been observed growing on plastics. The study, published in Environmental Science & Technology, reveals that a specific bacterium within this family can degrade plastic to use it as a food source.
The process involves the bacteria breaking down the plastic into nanoplastics before secreting an enzyme that further degrades it. This degradation allows the bacteria to utilize carbon atoms from the plastic as nourishment. Ludmilla Aristilde, who led the study, stated, "We have systematically shown, for the first time, that a wastewater bacterium can take a starting plastic material, deteriorate it, fragment it, break it down and use it as a source of carbon."
Aristilde is an associate professor at Northwestern's McCormick School of Engineering and is involved with several research institutes. The study was co-authored by Rebecca Wilkes and Nanqing Zhou from Aristilde’s lab.
The research builds on previous work concerning Comamonas testosteroni's ability to metabolize simple carbons from broken-down plants and plastics. The team focused on polyethylene terephthalate (PET), commonly used in food packaging and beverage bottles. PET is known for its resistance to breakdown and contributes significantly to global plastic pollution.
“It’s important to note that PET plastics represent 12% of total global plastics usage,” Aristilde said. “And it accounts for up to 50% of microplastics in wastewaters.”
To understand how C. testosteroni interacts with PET, researchers used various theoretical and experimental methods. They grew the bacterium on PET films and pellets and used microscopy to observe changes over time. They also examined surrounding water for nano-sized plastic fragments and identified tools within the bacteria aiding in PET degradation.
“In the presence of the bacterium, the microplastics were broken down into tiny nanoparticles of plastics,” Aristilde explained.
The study also explored how certain enzymes play a crucial role in this process. Collaborators at Oak Ridge National Laboratory prepared bacterial cells lacking these enzymes, resulting in diminished or lost ability to degrade plastic.
This discovery not only holds potential for developing environmental solutions but also enhances understanding of how plastics change during wastewater treatment processes.
“Wastewater is a huge reservoir of microplastics and nanoplastics,” Aristilde noted.
The research was supported by the National Science Foundation under award number CHE-2109097.