Ocean Bacterial Communities Collaborate to Break Down Biodegradable Plastics

The global plastic waste crisis continues to grow, with more than half of all produced plastic either ending up in landfills or directly released into the environment. Biodegradable plastics have emerged as a potential solution, but understanding exactly how these materials break down in natural environments has remained elusive. New research from MIT has taken a significant step forward in this area, revealing how different bacterial species collaborate to fully degrade a common type of biodegradable plastic.

"There is a lot of ambiguity about how long these materials actually exist in the environment," says lead author Marc Foster, a PhD student in the MIT-WHOI Joint Program. "This shows plastic biodegradation is highly dependent on the microbial community where the plastic ends up. It's also dependent on the plastics — the chemistry of the polymer and how they're made as a product. It's important to understand these processes because we're trying to constrain the environmental lifetime of these materials."

A Collaborative Approach to Plastic Degradation

Unlike previous studies that focused on single microbial organisms or provided only snapshots of bacterial communities, the MIT research team took a more detailed approach to understand the specific roles of individual bacteria in the degradation process. They studied an aromatic aliphatic co-polyester, a type of biodegradable plastic commonly used in shopping bags, food packaging, and agricultural applications where it's used as soil cover to prevent weeds and retain moisture.

The researchers began by placing samples of this plastic at different depths in the Mediterranean Sea, allowing natural bacterial communities to form biofilms around the material. These samples were then transported to MIT, where the team isolated as many bacterial species as possible. From these isolates, they identified 30 bacterial species that continued to grow in abundance on the plastic surface.

Using carbon dioxide production as a measure of plastic degradation, the researchers systematically tested each bacterial species individually. This process revealed a critical finding: no single bacterium could fully degrade the plastic on its own.

Key Players in the Degradation Process

The researchers identified one bacterium, Pseudomonas pachastrellae, that could depolymerize the plastic compounds, breaking them down into the three chemical components of the plastic: terephthalic acid, sebacic acid, and butanediol. However, this bacterium couldn't consume all three components by itself.

Through further testing, the team exposed each bacterial isolate to each chemical component, finding that while no single bacterium could consume all three components, several species could consume one or two of them individually. This suggested a complementary metabolic strategy within the bacterial community.

"It's really rare for a single bacterium to carry out the full degradation process because it requires a significant metabolic burden to carry all of the enzymatic functions to depolymerize the polymer and then use those chemical subunits as a carbon and energy source," Foster explains.

The researchers then selected five bacterial species based on their complementary breakdown abilities and demonstrated that this small group exhibited the same ability to fully degrade the plastic as the original 30-member community. When they removed any one of these five bacteria, the degradation rate decreased significantly, confirming each species played a critical role in the process.

Plastic-Specific Microbial Communities

An important finding from the research was that the five-bacteria community couldn't effectively degrade a different type of plastic, suggesting that microbial communities may be specialized for specific plastic chemistries.

"It highlights that the microbes living where this plastic ends up are going to dictate the plastic's lifetime," Foster notes. "Different environments have different microbial communities, which means the same plastic might degrade at different rates depending on where it ends up."

This plastic-specific degradation has significant implications for managing plastic waste. A biodegradable plastic that breaks down quickly in one marine environment might persist for much longer in another, depending on the local microbial community composition.

Methodological Advancements

The research team, which included MIT researchers, Woods Hole Oceanographic Institute scientists, and researchers from BASF (the chemical company that produces the studied plastic), developed a novel approach to isolate and characterize the specific bacterial functions in plastic degradation.

"Most studies wouldn't be able to identify the specific bacteria that's controlling each complementary mineralization process," Foster says. "Here we can say this bacteria controls degradation, these bacteria handle mineralization, and then we show the function of each bacteria and show that together, they can remove the entire polymer."

The methodology involved isolating bacterial species from environmental samples, individually testing their degradation capabilities, and then systematically combining them to identify the minimal functional community. This approach provides a more detailed understanding of the microbial processes involved in plastic biodegradation than previous methods.

Implications for Sustainable Materials and Recycling

The findings have several important implications for both the development of more sustainable materials and the creation of new recycling systems. By understanding which bacterial species and metabolic functions are most effective at degrading specific plastics, researchers can:

1. Design plastics that are more easily biodegradable in targeted environments
2. Develop microbial inoculants that can accelerate plastic degradation in specific settings
3. Create engineered microbial communities for more efficient plastic recycling
4. Better predict the environmental lifetime of biodegradable plastics

"Without knowing the specifics of different degradation processes, we won't be able to accurately predict the lifetime of these materials and better control that degradation," Foster explains.

Future Research Directions

Building on this foundational work, Foster is now exploring what makes successful bacterial pairs for faster plastic consumption and how enzymes dock on plastic particles to initiate and continue degradation. This research could lead to more effective strategies for managing plastic waste.

The study was supported by the MIT Climate and Sustainability Consortium and BASF SE, with partial support from the U.S. National Science Foundation Graduate Research Fellowship Program. The full research paper, "Complementary Bacterial Functions Enhance Mineralization of Aromatic Aliphatic Copolyesters within a Marine Microbial Consortium," was published in the journal Environmental Science and Technology.

As plastic production continues to increase globally, research like this becomes increasingly important. Understanding how natural systems break down these materials, even biodegradable ones, is crucial for developing effective waste management strategies and creating truly sustainable alternatives to conventional plastics.

For more information on this research, you can explore the MIT-WHOI Joint Program or the Department of Civil and Environmental Engineering at MIT. The research team's findings also connect to broader efforts at MIT addressing sustainability challenges, including work by Desirée Plata on sustainable materials and Otto Cordero on microbial ecology.