Sciences

Bio Major Breeds Microbes That Eat Plastic

Hungry bacteria thrive on plastic water bottles, opening up the possibility of using microorganisms to fight pollution.

By Chris Lydgate ’90 |

Bio major Morgan Vague ’18 has isolated and bred three strains of bacteria that consume and degrade polyethylene terephthalate (PET)—the ubiquitous plastic used in textiles, packaging, and soft-drink containers—opening up the tantalizing possibility of using microbes to fight pollution.

PET is an environmental nightmare. The plastic is biologically inert, notoriously resilient, and takes years, even centuries, to break down. An estimated 480 billion plastic bottles are manufactured every year, and after they have served their purpose many of them wind up in landfills, rivers, and oceans—the infamous Pacific trash vortex is currently the size of Texas.

BIRTH OF A COLONY. This striking image reveals an unusual sight—colonies of bacteria growing on a strip of PET plastic. The lobed structures in the center of the image are Bacillus cereus and Pseudomonas putida. The fluffy stuff on the bottom right is extracellular polymeric substance, a sort of foundation that bacteria lay down when colonizing a surface that enables them to form a living community called a biofilm. This material is a telltale clue that the bacteria are actually digesting the plastic. Another clue is the presence of pili—the spindly structures poking out from the colonies. These are small appendages that the bacteria use to attach to surfaces and begin colonizing. [PHOTO CREDIT: Scanning electron microscopy image is courtesy of Claudia S. López, PhD, Director of the Multiscale Microscopy Core at Oregon Health & Science University.]

But biologists at Reed have recruited an unlikely ally in the fight against plastic pollution—bacteria. Certain strains of bacteria produce lipase, a fat-digesting enzyme that can break down plastic molecules and render them palatable—in theory, anyway.

“The problem for most bacteria is that PET is a big, tough molecule with a lot of weird components,” says Morgan, who performed the research for her senior thesis. “Lipase is kind of like marinade on a steak. The bacteria squirts out the lipase and the lipase breaks the plastic into bite-size pieces.”

“These are very significant results,” says Prof. Jay Mellies, who supervised Morgan’s research. “It points the way towards a biological means of degrading plastic pollution.”

At the beginning of her quest, Morgan went hunting for microbes in locations with high levels of petroleum pollution, on the theory that those bacteria were most likely to have evolved biological mechanisms for digesting plastic. She traipsed around refineries in her hometown of Houston, Texas, digging up samples of soil, sand, and water around Galveston Bay. She snuck her samples into a refrigerated bag on her flight back to Portland, hoping that airport security screeners wouldn’t freak out. (They didn’t.)

Then she began the long, laborious process of screening her samples for lipase. Out of roughly 300 separate strains of bacteria, she identified 20 that produced the enzyme; three of these boasted high levels of lipase.

Bio major Morgan Vague ’18 brandishes test tube teeming with plastic-eating bacteria.

Then came the acid test. Morgan put three test tubes of bacteria on a forced diet of solid plastic, consisting of strips she cut out of old bottles of Nestle water that she bought at Safeway. With no other source of nourishment, the bacteria had a stark choice—eat plastic or die. Over the course of several weeks, she anxiously monitored the colonies for signs of growth.

The first glimmer of hope came when she noticed a tiny colony of bacteria forming on the surface of a strip of PET—suggesting that the microbes might consider the plastic toothsome. Then, on a Monday afternoon, she peered through a microscope and noticed that the colony was generating a fluffy structure known as extracellular polymeric substance—a telltale sign that it was thriving.

“I felt like I was on top of a mountain, shouting with joy,” she says. “I’d sunk so much time and energy into this project, and I didn’t know if it would work.”

The three substrains of bacteria are Pseudomonas putida, Bacillus cereus, and a hitherto unknown strain tentatively known as Pseudomonas morganensis, since Morgan appears to be the first researcher to identify it.

Prof. Mellies, a microbiologist who focuses on infectious diseases, says that supervising the project was both a joy and a challenge, because he had to go beyond his comfort zone. “These kinds of projects really push us as professors,” he says. “It’s great because it means that we learn together.”

For her thesis, Morgan was honored with the illustrious Class of ’21 Award, which recognizes “creative work of notable character, involving an unusual degree of initiative and spontaneity.”

Morgan transferred to Reed from Houston Community College, intending to study neuroscience. Then she took Intro Bio. “I fell in love with biology right then,” she says. “And then Prof. Jay Mellies’ class on microbiology literally changed my life.”

“As hard as it has been—and Reed has been incredibly difficult at times—this experience is like no other. The suport I’ve gotten, the mentoring, the opportunity—there’s no other school where an undergrad could do a project like this. I’m so grateful to Reed for giving me a chance.”

Morgan will spend the summer at Reed experimenting with ways to speed up the bacterial digestion process—right now it takes months for the bacteria to significantly degrade PET—and see if it can be deployed on an industrial scale.

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