Tough plastic-killer bacteria discovered in wastewater by US researchers

Among all plastic waste, PET is particularly problematic due to its durability and resistance to degradation.

It is widely used in food packaging and beverage bottles. Once discarded, it can remain in the environment for decades, harming wildlife and contaminating water sources.

“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 Ludmilla Aristilde, who led the study. 

“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,” Aristilde added.

The breakdown process

Researchers have identified the hidden power of Comamonas testosteri bacterium: it feeds on plastic waste. It is an environmental microorganism found in urban waterways and wastewater. 

Although the bacterium has been actively degrading plastic for a long time, its role in this process remained unrecognized until now.

The bacteria’s ability to degrade plastic is mediated by a combination of physical and biochemical processes.

The bacterium works by first chewing the plastic into tiny pieces. The organisms then release an enzyme into action that further degrades the plastic, allowing the bacteria to absorb the carbon atoms as nutrients.

These underlying processes were elucidated through a combination of theoretical and experimental methods. For this, the team isolated bacterium from wastewater. They were then grown in laboratory conditions on PET substrates, simulating their natural environment.

Using advanced microscopy techniques, the researchers closely examined the changes on the surface of the plastic material. The surrounding water was carefully analyzed to look for evidence of plastic degradation as well as the presence of nanoplastics. 

Simultaneously, they examined the internal structure of the bacteria to identify the mechanisms involved in plastic breakdown.

“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 which join together to form polymers. These small units are a bioavailable source of carbon that bacteria can use for growth.”

Role of enzyme

Aristilde’s team further identified a specific enzyme used by the bacteria to break down PET. To confirm the enzyme’s role in plastic degradation, they created bacterial cells without this enzyme and found that their ability to degrade plastic was significantly reduced or lost.

The authors highlight that nanoplastics can also be created in wastewater treatment plants by bacteria.

“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,” Aristilde noted. 

As per the press release, PET makes up 12% of all plastic in use and 50% of microplastics in wastewater. Hence, its safe disposal is a major concern.

This discovery could lead to new bacteria-based ways to clean up plastic waste from water bodies.

The findings were published in the journal Environmental Science & Technology.