Biologists at Reed College are developing bacterial colonies that can break down plastic pollution.
By Chris Lydgate ’90
March 18, 2021
It’s tough, it’s cheap and it’s everywhere. Polyethylene terephthalate (PET) is found in running shirts, carpet fibers, curtains, solar panels, tennis balls, microwaveable containers and plastic bottles – approximately 500 billion bottles are made from PET each year. But the very qualities that make PET so useful also make it an environmental nightmare. Its incredible durability means it will last for decades, clogging rivers, beaches, forests and waterways. According to a, about 8 million tons of plastic enter the oceans every year 2015 paper a sciencefueling the infamous Pacific Garbage Patch, which is currently the size of Texas.
To tackle this gargantuan problem, researchers at Reed College recruit a tiny ally.
In a landmark article published in mSpherethe open source journal of the American Society for Microbiology, Prof. Jay Mellies and students at Reed reported Colonies of bacteria capable of degrading PET. Remarkably, the colonies are not made up of a single species, but rather a consortium of five different species of bacteria that work together synergistically to consume PET and convert it into an energy source.
“What is new about our work is that we are using a group of bacteria to biodegrade PET plastic, whereas most efforts have so far focused on single, isolated enzymes for this purpose,” says Prof. Mellies.
The genesis for the project came from bio major Morgan Vague ’18, who investigated the relationship between bacteria and plastic for her diploma thesis with Prof. Mellies. She dug up samples of dirt from around Galveston Bay, Texas, to see if bacteria there might have evolved the ability to feed on hydrocarbons. She tried growing bacteria on broken water bottles; most died, but some stubbornly clung to life. Since PET is the only source of nutrition, she reasoned, it has to digest the plastic.
Prof. Mellies was enthusiastic. PET is notoriously non-biodegradable. Chemically, it’s a polymer made up of long, tough strands of ethylene glycol and terephthalic acid monomers, all tangled together. These strands give PET its durability; they also make it virtually impervious to biological reactions. But somehow the bacteria had found a way to break it down.
With the support of a grant from the National Science Foundation, Prof. Mellies and a new generation of students delved deeper into the phenomenon. They started by taking a closer look at how bacteria produce hydrolases, enzymes that bacteria (and other organisms) use to digest food.
Hydrolases are the molecular equivalent of scissors that can break up long, complex molecules for bacteria to ingest. PET polymers are much longer and more resilient than any food source that bacteria are likely to encounter in the natural environment. But bacteria are very adaptable. Given the right conditions, could a colony crank up the production of extra-hot enzymes and cut through the PET? After all, these chains are teeming with high-energy molecules that bacteria can use as food.
The Reed team worked with 192 separate colonies of soil bacteria and spent arduous months culturing them on PET. The process was excruciatingly slow. But after an eight-week trial, they found that the PET in one of their samples had lost 3% of its mass. The bacteria had eaten it. Under the microscope, the students saw tiny holes where the microbes had chewed through the PET.
Even more notably, the successful sample contained five different strains of bacteria living side by side, with some strains breaking down the PET into components that other strains could digest, and so on.
“These bacteria cooperate,” says Prof. Mellies. “It’s crazy, but they work together to break down the polymers.”
The concept of microbial symbiosis is not exactly new, but it represents a new frontier in microbiology. Since 1876, when the German biologist Robert Koch determined that the germ Bacillus anthracis was the cause of anthrax, researchers have focused on isolating individual organisms to pinpoint their characteristics. However, different types of microorganisms often live together in the environment and there is reason to believe that they can co-evolve. In fact, Prof. Mellies points to a 2001 publication by researchers in Japan who found symbiotic bacterial colonies that thrive in wastewater. “It was significant work,” he says. “I was so thankful to find this.”
Having determined that their consortium can indeed degrade PET, the Reed College team is now focused on the next step: finding ways to make the process more efficient. The genetic pathways underlying hydrolase production and PET degradation are not yet fully understood, but with new tools such as metagenomic sequencing, Prof. Mellies believes Reed students can increase production of enzymes that degrade PET and accelerate the evolution of bacteria. The potential benefit is huge – not only for fighting pollution, but also for harnessing microbial symbiosis for other problems.
Tags: Academics, Cool Projects, Editor’s Picks, Climate, Sustainability, Environmental, Professors, Research, Thesis