Wastewater bacteria can breakdown plastic for food
Finding could lead to bioengineering solutions to clean up plastic waste
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Comamonas bacteria live in wastewater, where they break down plastic waste for food.
view moreCredit: Ludmilla Aristilde/Northwestern University
Researchers have long observed that a common family of environmental bacteria, Comamonadacae, grow on plastics littered throughout urban rivers and wastewater systems. But what, exactly, these Comamonas bacteria are doing has remained a mystery.
Now, Northwestern University-led researchers have discovered how cells of a Comamonas bacterium are breaking down plastic for food. First, they chew the plastic into small pieces, called nanoplastics. Then, they secrete a specialized enzyme that breaks down the plastic even further. Finally, the bacteria use a ring of carbon atoms from the plastic as a food source, the researchers found.
The discovery opens new possibilities for developing bacteria-based engineering solutions to help clean up difficult-to-remove plastic waste, which pollutes drinking water and harms wildlife.
The study will be published on Thursday (Oct. 3) in the journal Environmental Science & Technology.
“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 Northwestern’s 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.”
An expert in the dynamics of organics in environmental processes, Aristilde is an associate professor of environmental engineering at Northwestern’s McCormick School of Engineering. She also is a member of the Center for Synthetic Biology, International Institute for Nanotechnology and 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 Aristilde’s lab. Several former graduate and undergraduate researchers from the Aristilde Lab also contributed to the work.
The pollution problem
The new study builds on previous research from Aristilde’s team, which unraveled the mechanisms that enable Comamonas testosteri to metabolize simple carbons generated from broken down plants and plastics. In the new research, Aristilde and her team again looked to C. testosteroni, which grows on polyethylene terephthalate (PET), a type of plastic commonly used in food packaging and beverage bottles. Because it does not break down easily, PET is a major contributor to 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.”
Innate ability to degrade plastics
To better understand how C. testosteroni interacts with and feeds on the plastic, Aristilde and her team used multiple theoretical and experimental approaches. First, they took bacterium — isolated from wastewater — and grew it on PET films and pellets. Then, they used advanced microscopy to observe how the surface of the plastic material changed over time. Next, they examined the water around the bacteria, searching for evidence of plastic broken down into smaller nano-sized pieces. And, finally, the researchers looked inside the bacteria to pinpoint tools the bacteria used to help degrade the PET.
“In the presence of the bacterium, the microplastics were broken down into tiny nanoparticles of plastics,” Aristilde said. “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.”
After confirming that C. testosteroni, indeed, can break down plastics, Aristilde next wanted to learn how. Through omics techniques that can measure all enzymes inside the cell, her team discovered one specific enzyme the bacterium expressed when exposed to PET plastics. To further explore this enzyme’s role, Aristilde asked collaborators at Oak Ridge National Laboratory in Tennessee to prepare bacterial cells without the abilities to express the enzyme. Remarkably, without that enzyme, the bacteria’s ability to degrade plastic was lost or significantly diminished.
How plastics change in water
Although Aristilde imagines this discovery potentially could be harnessed for environmental solutions, she also says this new knowledge can help people better understand how plastics evolve in wastewater.
“Wastewater is a huge reservoir of microplastics and nanoplastics,” Aristilde said. “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. 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 study, “Mechanisms of polyethylene terephthalate pellet fragmentation into nanoplastics and assimilable carbons by wastewater Comamonas,” was supported by the National Science Foundation (award number CHE-2109097).
Journal
Environmental Science & Technology
Method of Research
Experimental study
Subject of Research
Cells
Article Title
Mechanisms of polyethylene terephthalate pellet fragmentation into nanoplastics and assimilable carbons by wastewater Comamonas
Article Publication Date
3-Oct-2024
Plastic-eating enzyme identified in wastewater microbes
Plastic pollution is everywhere, and a good amount of it is composed of polyethylene terephthalate (PET, ♳). This polymer is used to make bottles, containers and even clothing. Now, researchers report in ACS’ Environmental Science & Technology that they have discovered an enzyme that breaks apart PET in a rather unusual place: microbes living in sewage sludge. The enzyme could be used by wastewater treatment plants to break apart microplastic particles and upcycle plastic waste.
Microplastics are becoming increasingly prevalent in places ranging from remote oceans to inside bodies, so it shouldn’t be a surprise that they appear in wastewater as well. However, the particles are so tiny that they can slip through water treatment purification processes and end up in the effluent that is reintroduced to the environment. But effluent also contains microorganisms that like to eat those plastic particles, including Comamonas testosteroni — so named because it degrades sterols like testosterone. Other bacterial species, including the common E. coli, have previously been engineered to turn plastic into other useful molecules. However, C. testosteroni naturally chews up polymers, such as those in laundry detergents, and terephthalate, a monomer building block of PET. So, Ludmilla Aristilde and colleagues wanted to see if C. testosteroni could also produce enzymes that degrade the PET polymer.
The team incubated a strain of C. testosteroni with PET films and pellets. Although the microbes colonized both shapes, microscopy revealed that the microbes preferred the rougher surface of the pellets, breaking them down to a greater degree than the smooth films. To better simulate conditions in wastewater environments, the researchers also added acetate, an ion commonly found in wastewater. When acetate was present, the number of bacterial colonies increased considerably. Though C. testosteroni produced some nano-sized PET particles, it also completely degraded the polymer to its monomers — compounds that C. testosteroni and other environmental microbes can use as a source of carbon to grow and develop, or even convert into other useful molecules, according to the team.
Next, the researchers used protein analysis to identify the key enzyme that gives this microbe its plastic-eating abilities. Though this new enzyme was distinct from previously described PET-busting enzymes based on its overall protein sequence, it did contain a similar binding pocket that was responsible for PET breakdown. When the gene encoding for this key enzyme was placed into a microbe that doesn’t naturally degrade PET, the engineered microbe gained the ability to do so, proving the enzyme’s functionality. The researchers say that this work demonstrates C. testosteroni’s utility for upcycling PET and PET-derived carbons, which could help reduce plastic pollution in wastewater.
The authors acknowledge funding from the U.S. National Science Foundation, the U.S. Department of Energy, the Office of Energy Efficiency and Renewable Energy, the Advanced Materials and Manufacturing Technologies Office, and the Bioenergy Technologies Office as part of the BOTTLE Consortium.
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Journal
Environmental Science & Technology
Article Title
“Mechanisms of Polyethylene Terephthalate Pellet Fragmentation into Nanoplastics and Assimilable Carbons by Wastewater Comamonas”
Article Publication Date
3-Oct-2024
Scientists develop novel method for strengthening PVC products
New method may mean less microplastic pollution
Ohio State University
COLUMBUS, Ohio – Researchers have developed a way to make one type of plastic material more durable and less likely to shed dangerous microplastics.
The study identified a secure way to attach chemical additives to polyvinyl chloride (PVC).
Found in everything from toys, construction supplies and medical packaging, PVC plastics currently rank third among the most used plastics worldwide. Despite its widespread use, pure PVC is brittle and sensitive to heat, and manufacturers can only utilize it after stabilizing its properties with other chemicals.
However, these additives, or plasticizers, are only a short-term fix for stabilizing PVC. Over time, plasticizers leach from the plastics, which allows the material to deteriorate into potentially hazardous organics and microplastics. Now, a team led by Christo Sevov, the principal investigator of the study and an associate professor in chemistry and biochemistry at The Ohio State University, found that using electricity to permanently affix those chemical additives can prevent such unwanted reactions.
“Instead of mixing in those chemicals, our method involves chemically bonding the plasticizer compound directly to PVC by grafting them onto the backbone of the polymer,” said Sevov.
Altering PVC molecules in this way allows for them to become more durable and resistant to chemical changes, eventually leading to materials with more robust properties.
“This is really one of the few examples that we have where there’s this much control over changing the properties of PVC,” said Sevov. “So this is the first step in controllably modifying PVC to give it properties you’re interested in, whether it’s hard, stretchy or soft.”
The team did run into some challenges; synthetic polymer modifications often fail because the reactions were originally developed for small-molecule analogs, not big-molecule analogs such as pure PVC. To solve this, researchers optimized the catalyst they used in their process, and through trial and error, were able to overcome the issues that arise when editing big molecules.
The study was recently published in the journal Chem.
Outside of making leaps in organic chemistry, the team’s work also has implications for the environment, as putting a cap on how quickly plastics degrade can do much to curb the release of microplastics — tiny pieces of plastic debris — into our surroundings.
Today, scientists know that these particles, which have been found to pollute the air, water and our food supply, are harmful both to humans and wildlife. The average person likely ingests between 78,000 and 211,000 of these particles every year.
But as experts are beginning to understand the long-term impact microplastics have on Earth, organic chemists are racing to find ways to phase them out of everyday life, said Sevov.
“Many chemists are shifting their efforts to studying big molecules and developing new chemistries for upcycling, recycling and modifying well-known polymers,” he said. For example, trying to recycle PVC products can cause further degradation to the material due to the high temperatures it takes to convert plastic into something else, so the process isn’t very efficient.
But using Sevov’s method, “You can potentially reuse the material many, many more times before it really begins to fall apart, improving its lifetime and reusability,” he said.
In the future, more control over which materials will be safe for consumers will come once efforts to fix PVC leakage can be reliably scaled up, something that the study emphasizes that, at the moment, is possible with their method alone.
“There’s no better way to do this on the scale you would need for commercial PVC modification because it is an immense process,” said Sevov. “There’s still a lot to play around with before we solve the microplastic situation, though now we’ve laid the groundwork for how to do it.”
Other Ohio State co-authors include Jordan L.S. Zackasee, Valmuri Srivardhan, Blaise L. Truesdell and Elizabeth J. Vrana. This work was supported by the Department of Energy’s Early Career Research Program.
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Contact: Christo Sevov, Sevov.1@osu.edu
Written by: Tatyana Woodall, Woodall.52@osu.edu
Journal
Chem
Method of Research
Experimental study
Article Title
Electrocatalytic grafting of polyvinyl chloride plastics
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