FROM DECADES TO DAYS:
Building Microbes that Eat
Photo: panaramka / iStock.com
More than 4.9 billon metric tons of soda bottles, grocery bags and other plastic waste now reside in the world’s landfills or pollute the natural environment—a number that could grow (according to one study) to 12 billion metric tons by 2050.
One reason for this growth: Plastic can take a century or more to fully decay. However, a team of engineers and biologists from Texas A&M University believe they can shorten the wait to a few days by finding and improving microbes that eat plastic.
Backed with a $2 million grant from the National Science Foundation, researchers at Texas A&M and the University of Oklahoma intend to dramatically reduce the volume of cups, bottles, bags and other plastic waste that pollute the environment, threaten wildlife, destroy habitats and harm human health.
The team of researchers from both universities has begun testing millions of microbes to identify the best candidates for genetic enhancement.
“First, we must identify which microbes are the most efficient at degrading plastic,” says Arum Han, principal investigator for the project and electrical engineering professor at Texas A&M. “Next, we ask: How do these microbes work? What makes them more efficient than the others? Which enzymes do they produce to degrade plastic? Then we will look for ways to improve these microbes to work even more efficiently.”
Specifically, the team is searching for microbes that naturally consume two common compounds that generate much of the world’s plastic waste:
Disposable cups, egg cartons and packing peanuts.
Soda bottles, grocery bags and other everyday products.
Illustrations: Ryan Farrell, Research Communications
Co-principal investigators for the project are chemical engineers and synthetic biologists Xuejun Zhu and Qing Sun, assistant professors in the College of Engineering; microbiologist Won-Bo Shim, professor in the College of Agriculture and Life Sciences, all at Texas A&M; and environmental microbiologist Aifen Zhou, University of Oklahoma.
The best of the best
The project team started by collecting a massive library of the most-promising microbes. Han’s laboratory is screening each candidate to weed out the pretenders.
“We need to conduct millions of single-cell tests as quickly as possible,” Han says. “This calls for something more sophisticated than the typical multi-well microplate.”
To get the job done, Han’s lab creates millions of micro-capsules, each large enough to hold a picoliter of fluid. (A picoliter is one trillionth of a liter; a raindrop can hold thousands of them.)
The lab then turns each micro-capsule into a tiny bioreactor by inserting some plastic particles, a small amount of nutrient and a single cell from the library of microbes.
“There’s almost no nutrient in the capsule,” Han says. “If we detect a fast-growing microbe, we know it must have found a way to use the plastic as a source of nutrient.”
Next, the lab selects the most productive microbes. Each will serve as a seed to produce millions of identical microbes that will undergo two more tests to confirm the first screening.
In the second test, each microbe is exposed to a micro-thin layer of plastic. To pass this test, the microbe much pierce the plastic layer, which the lab monitors with an electronic field.
A successful microbe will advance to a third test: an inspection of its activity under a microscope.
“Once we confirm these microbes—or groups of microbes—truly excel at degrading plastic, we will pass them back to the synthetic biologists on our project team,” Han says. “They will ask: ‘What can we do to these microbes to produce more of the plastic-degrading enzyme we want? How can we make that enzyme more active?’ In this way, we will create another library of microbes, and my lab will perform another round of screening.”
By repeating this process of testing candidates and enhancing their abilities, the research team intends to produce microbes that become more and more efficient at degrading plastic waste.
A FASTER WAY TO STUDY MICROBES
Scientists must study millions of microbes to identify the relatively few strains that excel at consuming plastic. To speed things up, researchers at Texas A&M produce millions of micro-capsules. Each contains a microbe, a nutrient and some plastic. These micro-capsules serve as little bioreactors, allowing investigators to quickly measure each microbe’s response. In this video, lab personnel show how they make the micro-capsules.
Video: Research Communications
In the long term, Han’s team aims to produce several bioengineered microbes that will work together to degrade plastic.
“Let’s say that plastic degradation is a five-step process,” Han says. “Then we may want to engineer five microbes, each of which is focused on one step of that process. We want those five microbes to work together as a synthetic community to degrade the plastic more efficiently. This would mimic nature. It’s not one superbug that degrades plastic. It is really several microbes performing different functions and working together in harmony.”
However, Han says, there’s more to the project than speeding up the degradation process. Ideally, this community of enhanced microbes would convert plastic waste into useful byproducts, like chemical precursors for producing industrial and consumer products.
This innovation could inspire a new industry: plastic-degradation factories that would deploy the microbes in a closed-loop system, like those used in a wastewater plant or a pharmaceutical factory.
“Plastic waste would go into the factory and useful products would come out,” Han says. “Any waste that leaves the factory will be sterilized so that no engineered microbes will be released into the wild.”
The "garbage patch" is a popular name for concentrations of marine debris in the North Pacific Ocean.
Video: Piotr Adamczyk / Shutterstock.com, Image: NOAA