Scientists discovered that bacteria commonly found in wastewater can break down plastic to turn it into a food source, a finding that researchers hope could be a promising answer to combat one of Earth’s major pollution problems.
In a study published Thursday in Environmental Science and Technology, scientists laid out their examination of Comamonas testosteroni, a bacteria that grows on polyethylene terephthalate, or PET, a plastic commonly found in single-use food packaging and water bottles. PET makes up about 12 percent of global solid waste and 90 million tons of the plastic produced each year.
“The machinery in environmental microbes is still a largely untapped potential for uncovering sustainable solutions we can exploit,” said Ludmilla Aristilde, senior author on the study and associate professor of civil and environmental engineering at Northwestern University.
Unlike most other bacteria, which thrive on sugar, C. testosteroni has a more refined palate, including chemically complex materials from plants and plastics that take longer to decompose.
The researchers are the first to demonstrate not only that this bacteria can break down plastic, but they also illuminate exactly how they do it.
Through six meticulous steps, involving complex imaging and gene editing techniques, the authors found that the bacteria first physically break down plastic by chewing it into smaller pieces. Then, they release enzymes — components of a cell that speed up chemical reactions — to chemically break down the plastic into a carbon-rich food source known as terephthalate.
Nanqing Zhou, a lead author on the study and postdoctoral researcher, compared the bacteria’s consumption of plastic to how people eat cows.“If you want to eat beef, you need to cut [it] into different parts, and some parts you can eat, some parts you cannot,” Zhou said. “You process it into different pieces of steak, and then you cook, and afterwards you need to cut [it] into smaller pieces before you eat and digest.”
The authors studied C. testosteroni’s eating habits so closely that they were able to pinpoint the specific enzyme that allows the germs to turn inedible plastic into a palatable, carbon-rich treat.
To confirm their finding, they removed the gene that was responsible for creating that enzyme and saw a significant reduction in C. testosteroni’s ability to break down plastic.
Though the bacteria are promising tools for combating pollution, they are not quite ready to be thrown into wastewater treatment plants and landfills as a cleanup crew.
“The way we want the plastic to be broken down is a lot faster than the bacteria really needs it to be broken down,” said Rebecca Wilkes, a lead author on the study and postdoctoral researcher at the National Renewable Energy Laboratory.The bacteria take a few months to break down chunks of plastic, according to Wilkes. As a result, if the bacteria are going to be efficient tools, a lot of optimization needs to take place to speed up the rate at which they decompose pollutants. One approach is to promote bacterial growth by providing them with an additional food source, such as a chemical known as acetate.
The study adds another tool to our environmental protection toolbox. Plastic pollution is a big problem, but not an insurmountable one, according to Timothy Hoellein, a biology professor at Loyola University Chicago.
“There’s a lot of different kinds of plastic, and there are just as many potential solutions to reducing the environmental harm of plastic pollution,” Hoellein said. “We’re best positioned to pursue all options at the same time.”
