Comamonadacae is a group of bacteria commonly found on plastics in aquatic environments. Recent research has revealed that a specific type of bacterium from this family can decompose plastic to obtain nutrients. The scientists also identified the enzyme responsible for this plastic degradation. This breakthrough paves the way for new bacterial engineering strategies aimed at tackling persistent plastic pollution.
For quite some time, scientists have noted that the Comamonadacae family of bacteria thrives on plastics scattered across urban waterways and sewage systems. However, the exact role these Comamonas bacteria play has been elusive.
Recently, researchers from Northwestern University found that cells of a certain Comamonas bacterium consume plastic as a food source. They start by breaking the plastic down into smaller fragments known as nanoplastics. Next, they release a unique enzyme that further processes the plastic. Ultimately, the bacteria utilize a ring of carbon atoms derived from the plastic as nourishment, according to their findings.
This discovery opens exciting avenues for creating engineering applications based on bacteria that could assist in the removal of stubborn plastic waste, which contaminates drinking water and endangers wildlife.
The findings will be published on Thursday (Oct. 3) in the journal Environmental Science & Technology.
“For the first time, we have clearly demonstrated that a wastewater bacterium can take an initial piece of plastic, degrade it, break it down, and then utilize it as a source of carbon,” stated Ludmilla Aristilde from Northwestern, who led the study. “It’s incredible that this bacterium can carry out this whole process, and we’ve pinpointed a crucial enzyme that facilitates the breakdown of plastic materials. This could be refined and utilized to help eliminate plastics from the environment.”
Aristilde specializes in the dynamics of organic materials in environmental processes and serves as an associate professor of environmental engineering at Northwestern’s McCormick School of Engineering. She is also affiliated with the Center for Synthetic Biology, the International Institute for Nanotechnology, and the Paula M. Trienens Institute for Sustainability and Energy. The study’s co-first authors are Rebecca Wilkes, a former Ph.D. student in Aristilde’s lab, and Nanqing Zhou, a current postdoctoral associate in her lab, along with contributions from several past graduate and undergraduate researchers from the Aristilde Lab.
The pollution problem
This recent study builds upon prior investigations by Aristilde’s team, which explored how Comamonas testosteri metabolizes simple carbon sources that result from degraded plants and plastics. In the current research, Aristilde and her colleagues focused on C. testosteroni, which feeds on polyethylene terephthalate (PET), a widely used plastic in food packaging and beverage containers. PET’s resistance to degradation makes it a significant contributor to plastic pollution.
“It’s crucial to highlight that PET plastics account for 12% of total global plastic consumption,” noted Aristilde. “Moreover, they contribute to up to 50% of microplastics found in wastewater.”
Innate ability to degrade plastics
To delve deeper into how C. testosteroni interacts with and feeds on plastic, Aristilde and her team employed various theoretical and experimental methods. Initially, they isolated the bacterium from wastewater and cultivated it on PET films and pellets. They then utilized advanced microscopy to observe changes in the plastic surface over time. Next, they analyzed the surrounding water for traces of plastic broken down into smaller nanoplastics. Finally, the researchers investigated the bacteria’s internal mechanisms to identify tools utilized for PET degradation.
“In the presence of this bacterium, microplastics were degraded into minuscule nanoparticles,” Aristilde explained. “We revealed that this wastewater bacterium naturally possesses the ability to degrade plastics down to monomers—small units that link together to form polymers. These monomers serve as a bioavailable carbon source that bacteria can utilize for growth.”
Once confirmed that C. testosteroni could indeed degrade plastics, Aristilde sought to understand the method. Using “omics” techniques that assess all enzymes within the cell, her team discovered one specific enzyme that the bacterium produced when exposed to PET plastics. To investigate the enzyme’s significance, Aristilde collaborated with scientists at Oak Ridge National Laboratory in Tennessee to create bacterial cells lacking this enzyme. Astonishingly, the bacteria lost or greatly reduced their ability to degrade plastic without that enzyme.
How plastics change in water
While Aristilde envisions this discovery could be leveraged for environmental solutions, she also believes it enhances understanding of how plastics evolve within wastewater.
“Wastewater is a vast reservoir of microplastics and nanoplastics,” Aristilde remarked. “Many assume that nanoplastics enter wastewater treatment facilities as nanoplastics. However, we are demonstrating that nanoplastics can form during wastewater treatment due to microbial activity. This is an important factor we must consider as society endeavors to comprehend the behavior of plastics throughout their journey from wastewater to rivers and lakes.”
The study, titled “Mechanisms of polyethylene terephthalate pellet fragmentation into nanoplastics and assimilable carbons by wastewater Comamonas,” received support from the National Science Foundation (award number CHE-2109097).
