Plastic-eating bacteria – what is it? Why is it important? And how does it work? Those are all questions we’ll answer in this video, but first some background.
Plastic – it’s all around us. From our water bottles, to the linings of our winter coats, to the bags we use to carry groceries, and even the pipes inside our houses.
Plastic was a revolutionary material! It has unique characteristics like being low-cost, light-weight, durable and flexible!
As a basic overview, plastic is a synthetic polymer made up of a variety of elements including carbon, oxygen, hydrogen, nitrogen, chlorine, sulfur, and more.
Synthetic simply means that plastic is created by humans, rather than found in nature. While polymer means plastic is composed on many repeats of some basic unit.
There are a variety of different types of plastic, each of which have different structures, are made of different combinations of elements, and are manufactured in different ways.
These types of plastic include polypropylene, or PP, and polyethylene, or PE, which make up more than 50% of plastic. There’s also polyethylene terephthalate, or PET, polyvinyl chloride (PVC) and polystyrene, PS or Styrofoam amongst many other kinds of plastic.
Given so many objects our world are made of plastic, it’s no surprise there is a lot of plastic produced every year. In 2018, almost 360 million metric tonnes of plastic were produced, That’s the equivalent of around 22,500 average two-story US homes or around 1.9 million cars worth of plastic. and that was just in one year!
The COVID-19 Pandemic has added to the production of plastic since much of the personal protective equipment we use is made of disposable plastic components. Every month around 129 billion face masks and 65 million gloves are being discarded around the world.
So what happens to all this plastic? There are three main outcomes. One is that the plastic ends up sitting in landfills. Two is that the plastic is burned or incinerated, however this leads to the release of toxins and hazardous fumes. Three is that the plastic is dumped into the oceans which can harm aquatic animals and may be broken into microplastics which can impact the food chain.
Recycling is also an option however, only around 10% of plastic is recycled worldwide indicating a need for a new solution.Enter plastic-eating bacteria!
Before we get into the specifics, we will briefly go over the basics about bacteria. To get a better understanding lets compare bacteria and humans.
While humans are made up of many cells, bacteria are all single-celled organisms. Human cells also contain membrane bound organelles, such as the mitochondria for energy or the nucleus to contain chromosomes. Bacteria have no membrane bound organelles within them. Finally, bacteria are unique in that their DNA floats freely in their cells unlike human DNA which is contained within the nucleus.
Now onto plastic eating bacteria specifically. As we learned earlier there are different types of plastic, such as PET, PP, PVC, and PS. Each type of plastic is degraded by a different bacteria. However, there are some overarching taxa, or groups, of bacteria that are involved in plastic degradation.
These include: Arthrobacter, Bacillus, Micrococcus, Pseudomonas, Corynebacterium, Streptomyces, Rhodococcus, and Nocardia.
In addition, extremophiles are another class of bacteria that may be useful for plastic degradation. These are bacteria that live in extreme environments, such as in extreme temperatures or places with very high or basic pH. Since the characteristics of plastic change at these extremes, it may become easier for bacteria to degrade it in these environments.
In particular there are four groups of extremophiles of interest: thermophiles, bacteria that live in very hot places, alkaliphiles, bacteria that live in very basic or high pH places, halophiles, bacteria that live in salty places, and psychrophiles, bacteria that live between -20 and +20˚C. In particular halophiles and psychrophiles could be extra useful in the ocean environment, as the sea has a high salt content and is normally around 5˚C.
While bacteria are able to degrade plastic, plastic has some characteristics that make it more difficult to degrade. First, plastic is hydrophobic, or resistant to water, which contributes to plastic’s low bioavailability.
Second, plastic has a high molecular weight which makes it hard to get plastic molecules across the cell membrane of the bacteria so that it can be degraded within it. This means that plastic must be depolymerized, or broken into smaller pieces, before it can cross the membrane of bacteria.
Third, plastic’s structure, a long-chain polymer, lacks the functional groups, specific combinations of elements, that are helpful to bacteria in their degradation
How does bacteria ACTUALLY degrade plastic?
Mechanisms of biodegradation can either occur directly by the microbe, using the plastic as a source of nutrients or through its release of enzymes, essentially breaking down molecules of plastic into its original building blocks.
First the microbe attaches to a polymer and colonizes. Through pH changes, its metabolic activity causes plastic cracks which challenges the polymers physical properties. This is known as biodeterioration.
Then enzymatic activity produced by the microorganism leads to the long polymer chain releasing oligomers which are molecules consisting of relatively fewer repeating parts. This is known as bio-fragmentation.
These oligomers enter the cell and are further degraded into single monomers which are mineralized into byproducts such as carbon dioxide and water!
When was plastic eating bacteria actually discovered?
Plastic degrading bacteria discoveries can date back to the early 2000’s when samples of different bacteria were isolated from soil samples and marine environments.
However, plastic “eating” bacteria first made headlines in 2016 when a group of researchers in Japan discovered Ideonella sakainesis. This strain was able to decompose or “eat” PET plastics. However, their discovery was limited as it exclusively degraded PET and did so at a very slow rate.
Later that year, scientists in Pakistan reported a fungus capable of degrading plastic.
In 2017, plastic-eating bacteria was isolated from an oil site in Texas. In 2018, scientists modified bacteria to degrade plastics within days in the UK and US.
In March 2020, German scientists discovered a new strain. In October 2020, the US and UK improved their discovery by combining 2 strains to create the “super enzyme”, capable of degrading plastics more efficiently.
After this research came out, a french firm, Carbios, began developing a demonstration plant which will be able to enzymatically degrade PET plastic at an efficient rate. This company is partnering with PepsiCo and Nestle. Their goal is to develop a bacteria which can break down large commercial amounts of plastic and recycle material back into their products.
Currently there are a number of active branches of associated research. The first involves screening - so looking at natural microbial communities exposed to plastics, particularly in soil, and sampling in attempt to isolate novel bacterium with plastic degrading properties - similarly to what was done in Osaka Japan and Texas.
Screening can also involve researchers analyzing DNA collected from various ecosystems to determine if genetic material from these environments indicate plastic degrading potential - meaning DNA which codes for enzymes capable of breaking down plastics.
What current research suggests is that the more an environment is exposed to plastic pollution, the greater its plastic degrading potential - which indicates evolutionary selective pressure.
Even though we are seeing selective pressure acting upon bacteria to degrade plastics, this is still a relatively new biological property when compared to microbes which have evolved to degrade organic material over millions of years - meaning they aren’t as efficient. Therefore, researchers are actively looking for ways to modify, or engineer, these enzymes to break down plastics faster.
In order for these bacteria to be useful and applicable worldwide, there must be a way to bioengineer them to degrade plastic at rates that are hundreds or thousands of times faster. Another interesting fact is that Plastic eating bacteria can also be used to break down clothing that is dumped in landfills by incorporating it with certain enzymes that break down cotton.
Although plastic-eating bacteria are useful in reducing the growth of plastic waste in oceans and landfills which is a good thing it comes with issues that may affect the environment.
Toxins are released as by-products by the plastic-eating bacteria to the environment. So you may be wondering oh the toxins might not even be that bad compared to the plastic accumulation problem that is present.
But apparently, These bi-products are actually potentially harmful to the environment even more than the accumulation of plastic waste and since the bacteria is lab-created the implications that are caused by the bi-products are still untested and unknown in the environment.
So what is the next step in research?
Since this is a relatively new topic there is still a lot that researchers don’t know. The ultimate goal is to address the challenges created by plastics.
To do this, researchers need to make these plastic degradation processes less costly and less time consuming. It is important for researchers to have a better understanding of polymer characteristics to improve microplastic characterization and could use molecular techniques to analyze the mechanisms related to microplastic degradation.
Finally, in order to propel this research into action, researchers must determine the potentially harmful side effects that could take place in real aquatic ecosystems.
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