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The unseen heroes to our plastic waste how a college student's graduate requirement may help save the environment

The creation of plastic was revolutionary: we created our own building blocks that could transform into thousands of uses. The economic benefits and adaptability of this strong yet lightweight material led the boom to the plastic era. However, we now stand on a world decorated by plastic mountains with plastic sprinkles in the ocean. But alas, plastic is still doing an amazing job at being indestructible! And not only do we not have enough space for plastic waste to take ten centuries to decompose, additives like Bisphenol A (BPA) pose direct harms to our hormonal system. Therefore, the question is how we dispose of the accumulated plastic soiling our environment and health.

Breaking it down.

The current solution to our plastic waste is recycling. However, there are still many limitations to recycling and it doesn’t solve the already existing piles of plastic waste. Thankfully, as disposable utensils and packaging are being produced, innovative minds are also growing and culturing solutions – quite literally.

Morgan Vague, Reed College Class of 2018 (photo by Nina Johnson)

Morgan Vague was a Biology major at Reed College in Portland, Oregon. As a native of Houston, Texas, Morgan recalls the major petroleum pollution in her hometown. And when it was time to pick a topic to investigate for her senior thesis, she took inspiration from her personal experience with plastic and her microbiology education to find bugs that can degrade plastic, emphasizing

“the crazy ways bacteria scavenge and find food and how quickly they can adapt to different environments.”

Under the guidance of her principal investigator and microbiology professor, Dr. Jay Mellies, Morgan looked to isolate plastic-eating bacteria in areas of high pollution. Such an environment potentially pushes for an evolved mechanism to make use of the abundance of plastic. With the soil samples she collected from her trip home, Morgan screened for bacteria with lipase, an enzyme suggested to be involved in plastic degradation from previous science research.

Numerous subsequent experiments then led her to the discovery of biofilms growing on PET plastic. Usually formed under stress like starvation, biofilms are a community of bacteria attached to a surface that collaborate with each other in order to survive. So when Morgan subjected her screened bacterial colonies to only have plastic as a carbon source, three strains of bacteria survived starvation by forming a biofilm that transformed plastic into a meal.

Specifically, the bacteria are able to cluster together in the biofilm and expel the previously mentioned lipases, the active ingredient of the biofilm. The lipase are able to break the plastic apart enough for the bacteria to get to the carbon backbone and use it as its food source. It can be thought of as a marinade that “tenderizes” the plastic. Another ingredient found in the biofilm may also help degrade the plastic. Biosurfactants, compounds alike detergents, produced by a Bacillus bacteria may have a role in assisting the plastic degradation process.

Image courtesy of Claudia S. López, PhD, Director of the Multiscale Microscopy Core at Oregon Health & Science University.

Through these bacteria’s “metabolic acrobatics” as Morgan describes, PETs no longer have to wait ten centuries to degrade but be taken care by microorganisms, the heroes we can’t even see.

The three strains of bacteria include: Bacillus cereus, Pseudomonas putida, and a novel Pseudomonas strain. Morgan had the opportunity to name it Pseudomonas morganensis. And surprisingly, these three added to an already existing list of plastic-degrading organisms. In 2016, Japanese researchers isolated Ideonella sakaiensis, a strain of bacteria also found to metabolize plastic. The mechanism of these discovered strains is fairly similar: they both use an alpha-beta hydrolase, which are biological catalysts that break chemical bonds by using water, such as lipases.

With all these discoveries of plastic-degrading bacteria, Morgan points out that they are much more common than we think. And our plastic waste may benefit from having more groups start exploring and collecting samples from polluted sites. “These bacteria are already out there in the environment doing that process, why not try to put them to work.”

Let's talk plastic.

So the degradation of plastic comes down to a whole bunch of C’s – that is carbon molecules. This name gets thrown around a lot, especially when talking about climate change. But as we are seeing, carbon itself isn’t bad! In fact, it is what makes life possible. We are made of carbon, we eat carbon to grow and survive just like Morgan’s bacteria. Instead, it is the fact that plastics are a bunch of carbon polymers that makes it so bad and hard to break down.

Carbon polymers are made by connecting carbons together to form a central chain, much like your bones making the skeleton that structures your body. However, unlike the individual carbon units of sugars, these long and strong carbon-carbon chains are not naturally present in nature because it takes an abundance of energy to connect a bunch of carbons together. The production of a plastic bottle requires 3.4 megajoules of energy. That is 812,620 calories and if you eat about 2,000 calories a day, that’ll last you more than a year.

Pictured are the skeletal formulas of different backbone structures for different types of plastic that determine how they can be reused or degraded. Each unlabelled angle in the structure represents a carbon molecule. The "n" refers to the number of repeating subunits within the bracket that join to make the plastic polymer. It is the increasing value of "n" that makes plastic so hard to break down.

Because it is not naturally found in nature, our environment has not evolved to process this material. When a piece of plastic is thrown away, usual decomposing organisms can’t exactly degrade it like it can degrade the sugars of an apple. This makes plastic durability something of a double-edged sword: it is a fantastically useful product but also incredibly difficult to naturally degrade like organic material.

And this is where Morgan’s research brings us hope. We now know that when needed, some bacteria can break up those long chains and take in plastic as food.

The feast.

Where do we go from here? Well, another Reed College senior is currently continuing this project for her own thesis. Knowing the main character for plastic degradation is the lipase, Cam Roberts is screening for their genetic components that control production and regulation. This is in hopes of upregulating those elements to speed up the bacteria’s metabolism of plastic. Morgan’s vision of this is a “big industrial scaled, contained, carbon free system where these bacteria can thrive on their sole food source of PET waste.”

Right now, the degrading ability of the three bacterial strains has only been tested on PET plastic. But as Professor Mellies points out, "there are many kinds of plastic and even within the same type of plastic, they are different because people use different plasticizers." This makes not only recycling more complicated, but also adds in more factors to how the mechanisms of metabolism can be used to degrade plastic. So, as we wait for a factory of bioremediation, what we can do is be cognizant of reducing our plastic use and the types of plastic being used.

-- Vicki Deng

Credits:

Created with images by Dustan Woodhouse - "The modern beach"

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