Biodegradable plastics have long been hailed as a beacon of hope in addressing the white pollution crisis. However, a critical question has remained unanswered: Once discarded into the ocean or soil, how long does it actually take for these plastics to completely disappear? And how exactly do environmental microbes "eat" them?
Now, researchers at the Massachusetts Institute of Technology (MIT) have taken a significant step toward unraveling this mystery. A new study published in the journal Environmental Science and Technology reveals, for the first time in detail, that marine bacteria do not work alone. Instead, they collaborate through a clear division of labor to completely break down a common type of biodegradable plastic.
“This shows plastic biodegradation is highly dependent on the microbial community where the plastic ends up,” says Marc Foster. Credit: MIT News; iStock
One Bacterium Can't Do It All; It Takes a Team
"There is a lot of ambiguity about how long these materials actually persist in the environment," notes Marc Foster, the study's lead author and a PhD student in the MIT-WHOI Joint Program. "Our research shows that the rate of plastic biodegradation heavily depends on the specific microbial community where the plastic ends up. The chemistry of the polymer and how the product is manufactured also play a decisive role."
In the past, much research on plastic degradation focused on single microbial organisms. However, Foster believes this is far from realistic. "It's incredibly rare for a single bacterium to carry out the entire degradation process," he explains. "The metabolic burden of carrying all the enzymatic tools needed to depolymerize the polymer and then metabolize the resulting chemical byproducts is simply too much for one organism to handle."
To mimic real-world conditions, the research team designed an ingenious experiment. In collaboration with BASF, the company that produces this type of plastic, they first submerged samples of the biodegradable plastic at various depths in the Mediterranean Sea, allowing native marine bacteria to naturally colonize the surface and form a biofilm. These samples were then sent to the MIT lab, where researchers isolated up to 30 species of bacteria that were thriving on the plastic.
Identifying the 'Cutter' and the 'Cleanup Crew'
To track the role of each bacterium, the researchers used carbon dioxide production (an indicator of complete plastic degradation) as a metric, analyzing the bacteria one by one. They discovered that a bacterium named Pseudomonas pachastrellae played a critical role. It acted as a "cutter," capable of cleaving the long polymer chains of the plastic into three basic chemical building blocks: terephthalic acid, sebacic acid, and butanediol.
However, this "cutter," while able to tear the plastic apart, could not digest the resulting fragments. The researchers then exposed the other bacteria to each of these three chemical components individually. They found that no single bacterium was a "universal digester" capable of consuming all three substances alone. Some specialized in terephthalic acid, while others preferred sebacic acid.
Based on these distinct "dietary preferences," the researchers carefully selected five bacterial species with complementary metabolic functions and assembled them into a miniature "synthetic community." The results of this five-member team's performance were striking: working in concert, they demonstrated the same ability to completely degrade the plastic into carbon dioxide as the original natural community of 30 bacteria.
"It worked much better than I thought it would," Foster recalls. "When I removed any single member from this team, the overall degradation efficiency dropped, showing that each plays an indispensable role. And when isolated alone, none could achieve the team's collective performance. This clearly indicates that complete degradation requires this functional complementarity."
Plastic Degradation Has a 'Local Flavor'
Interestingly, this highly efficient "team of five" was helpless when confronted with a different type of plastic. This suggests that the degradation capability of a microbial community is highly "customized"; a team specialized in breaking down one type of plastic may not be able to handle others.
Foster emphasizes that this highlights a crucial fact: the specific microbes present in the environment where a piece of plastic ends up directly determine its "lifespan." A shopping bag that might degrade within a few years in the Mediterranean Sea could have a vastly different decomposition timeline if it ends up in the North Atlantic, where the microbial community composition is different.
Towards a Future of 'Microbial Recycling'
While Foster acknowledges that the bacteria identified in this study may be specific to the Mediterranean region and limited to those that can be cultured in the lab, this research still represents a milestone in the field.
"Most studies can't tell us which specific bacterium controls which stage of the degradation process," Foster says. "Here, we can clearly point out that this bacterium is responsible for the initial cutting, and those bacteria handle the subsequent mineralization. We've shown the function of each and demonstrated that only by working together can they completely eliminate the entire polymer."
This research not only deepens our understanding of natural material cycles but, more importantly, opens the door to designing more environmentally friendly materials in the future and even developing novel "microbial recycling systems." Scientists might one day be able to assemble different microbes like a sports team, optimizing their configuration to efficiently convert plastic waste into valuable chemical feedstocks or energy.
In his ongoing PhD work, Foster is now exploring which factors contribute to more successful bacterial partnerships for faster plastic decomposition and how enzymes dock onto plastic particles to initiate the entire process.
This work was supported by the MIT Climate and Sustainability Consortium, BASF SE, and the U.S. National Science Foundation Graduate Research Fellowship Program.
About WebWire: WebWire is a leading internet news and press release distribution service since 1995.
