Wastewater bacteria break down plastic waste for food

Researchers have long known that a common family of environmental bacteria called Comamonadaceae thrive in urban rivers and wastewater systems where plastic litter is abundant. 

However, what exactly these bacteria are doing with the plastic has remained unclear until now.

A recent study led by Northwestern University has uncovered how cells of a Comamonas bacteria break down plastic to use as food. 

Bacteria and the issue of plastic waste

The researchers found that the bacteria first chew the plastic into small pieces, called nanoplastics. Then, they secrete a specialized enzyme that further breaks down the plastic. Finally, the bacteria feed on the carbon atoms from the plastic, using it as a food source.

This discovery opens up exciting new possibilities for creating bacteria-based solutions to tackle the growing problem of plastic waste, which contaminates drinking water and poses serious threats to wildlife.

Wastewater bacteria break down plastic 

Study lead author Ludmilla Aristilde is an associate professor of environmental engineering at Northwestern. 

“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,” said Aristilde. 

“It is amazing that this bacterium can perform that entire process, and we identified a key enzyme responsible for breaking down the plastic materials. This could be optimized and exploited to help get rid of plastics in the environment.”

Expanding on earlier research 

Aristilde, an expert in organic dynamics in environmental processes, led the study along with her team, including co-first authors Rebecca Wilkes and Nanqing Zhou. Several graduate and undergraduate researchers from Aristilde’s lab also contributed to the work.

This new research builds upon earlier work by Aristilde’s group, which explored how Comamonas testosteroni metabolizes simple carbons from broken-down plants and plastics. 

Bacteria and PET plastic

In this study, the team focused again on C. testosteroni, which is known to grow on polyethylene terephthalate (PET) – a type of plastic commonly found in food packaging and beverage bottles. 

PET is notorious for being difficult to break down and is a major contributor to plastic pollution worldwide.

“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.”

Watching bacteria degrade plastic

To better understand how C. testosteroni interacts with and feeds on plastic, Aristilde’s team used a range of experimental and theoretical approaches. 

First, they grew the bacteria – isolated from wastewater – on PET films and pellets. Using advanced microscopy, they observed how the plastic surfaces changed over time. 

The team also examined the surrounding water to detect plastic broken down into smaller nanoparticles. 

Finally, the researchers investigated the bacteria to identify the tools they use to degrade the plastic.

Transforming plastic into a carbon source 

“In the presence of the bacterium, the microplastics were broken down into tiny nanoparticles of plastics,” Aristilde explained. 

“We found that the wastewater bacterium has an innate ability to degrade plastic all the way down to monomers – small building blocks that join together to form polymers. These small units are a bioavailable source of carbon that bacteria can use for growth.”

A deeper understanding of the process 

Once the team confirmed that C. testosteroni could indeed break down plastics, they delved deeper into understanding how this process occurs. 

Using omics techniques to measure all enzymes inside the bacterial cells, they identified a specific enzyme that was expressed when the bacteria were exposed to PET plastic. 

Collaborators at Oak Ridge National Laboratory in Tennessee then prepared bacterial cells that lacked the ability to express this enzyme. Remarkably, the bacteria without this enzyme lost or significantly diminished their ability to degrade plastic.

Broader implications of the study

While this discovery could potentially lead to new environmental cleanup technologies, Aristilde also emphasized that the research provides valuable insights into how plastics change during wastewater treatment.

Aristilde noted that wastewater is a huge reservoir of microplastics and nanoplastics.

“Most people think nanoplastics enter wastewater treatment plants as nanoplastics. But we’re showing that nanoplastics can be formed during wastewater treatment through microbial activity,” Aristilde said.

“That’s something we need to pay attention to as our society tries to understand the behavior of plastics throughout its journey from wastewater to receiving rivers and lakes.”

The team’s findings highlight the importance of paying closer attention to how plastics behave and transform in environmental systems, with the potential for new strategies to mitigate plastic pollution on the horizon.

The study is published in the journal Environmental Science & Technology.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates.

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–