Can Bacteria Help us Get Rid of Microplastics?
My research will directly increase the knowledge we have around a relatively new topic in science: microplastics. In particular, I will try to answer a specific question: Do the surface properties that enhance bacterial attachment to chitin also enhance attachment to ordinary plastics surface and, if they do, is there a preference for a specific kind of material?
If you never heard of microplastics or chitin, you might be thinking: Why microplastics and chitin? What are microplastics? Why is it relevant to understand how bacteria attach to these compounds?
Microorganisms Degrade “Natural” Plastic
Chitin is a naturally occurring polymer (i.e., a “naturally occurring plastic”). It is a component of the exoskeleton of arthropods and of the cell wall of certain fungi. It is one of the most abundant polymers in nature, and therefore microorganisms can use chitin for some biological processes (hence biodegrading chitin) to obtain Carbon and Nitrogen, nutrients needed for their metabolic processes.
The Problem of Plastic …
On the other hand, we have industrial plastics, a relatively new type of material. The first industrial polymer from which there is an available record is vulcanised rubber, successfully produced by Charles Goodyear in 1839. The discovery of that first polymer gave birth to a new area in materials science: the plastics. However, it was not until 1953 when Karl Ziegler and Giulio Natta took a significant step by discovering a very diverse method to manufacture different kinds of polymers, which also turned out to be very cost-effective (for which they were awarded the Nobel Prize in Chemistry in 1963). From that moment, thousands of plastics have been discovered, with a broad range of amazing properties (such as heat resistance, oxygen impermeability, an unparalleled combination of mechanical strength and light weight, etc.), giving rise to what some scientists and engineers describe as “the era of plastics”. It is precisely due to this combination of amazing properties and low cost that plastics gradually replaced other materials in an endless number of industrial applications. Think of the packaging industry: After the 1960’s we have seen a massive proliferation of disposable plastic packagings replacing other materials in many cases, for instance, glass.
A PET bottle will take about 450 years to degrade.
The downside of that story is that, precisely due to their unusual properties, plastics are not easily degradable, persisting in nature for hundreds of years (if not recycled or disposed of correctly). It is commonly accepted that, for example, a PET bottle will take about 450 years to degrade. And we just started producing these materials about 70 years ago!
… and Microplastic Waste
in Our Environment
We now are more conscious about the damage that plastics cause to the environment: Probably most of you heard about a large plastic island that was formed in the ocean by an agglomeration of plastic waste. So what happens with all the plastic that we produced during the last 70 years, and we did not dispose of correctly? Well, a portion of those plastics ended up in aquatic environments, such as the ocean, or bodies of fresh water. Generally, during the degradation process (which started, but will take a long time!), polymer properties decay and they become less mechanically resistant.
When plastic particles are smaller than
5 mm, they are called microplastics.
Thus, plastic objects eventually break down into smaller bits, which is a form of erosion. When those smaller particles of plastic are smaller than 5 mm, they are called microplastics. It’s important to note though that erosion is only one source of microplastics. Some microplastics found in the environment were already produced in that size for different applications, such as the cosmetic industry: Different brands of shampoo, toothpaste, liquid soap, etc., used to add microplastics to their formulation due to their exfoliating effect (I say “used to” because they are now banned in many countries).
Same as with plastics, microplastics are also persistent organic pollutants. Additionally, they have the potential to bioaccumulate, which means that they can enter the food chain because of their tiny size. Think of a fish that swallows microplastic in the ocean: If some of those microplastics get attached to the flesh, we might end up eating those microplastics. Last year, a study carried out at the Medical University of Vienna proved the presence of microplastics in human stools.
Coming Back to Bacteria and Their Use Of Chitin …
Let’s go back to the first question: Why microplastics and chitin? Well, I mentioned at the beginning that chitin is used by different bacteria as a source of Carbon and Nitrogen. We know that when plastic materials, including microplastics, are released to the aquatic environment, a coating layer of inorganic and organic substances is formed, and microorganisms can attach to the surface. What if microplastics provide a “better” or “easier” source of Carbon and Nitrogen than chitin? If that were the case, microplastics might be affecting the balance of bacteria in different ecosystems.
… Or How Bacteria Might Help Us Clean Water polluted with Microplastics
However, it is not all bad news. If microplastics are indeed replacing chitin as a source of Carbon and Nitrogen, that could imply that bacteria could degrade microplastics! Understanding this phenomenon could help us actually use bacteria to clean bodies of water polluted with microplastics under controlled conditions.
If microplastics are indeed replacing chitin as a source of Carbon and Nitrogen, that could imply that bacteria could degrade microplastics.
This is, of course, a huge problem to solve (full of conjectures and question marks), and scientists recently started to break it down into smaller problems to understand the underlying mechanisms and all the potential implications (kind of like a puzzle). Restating what I mentioned at the beginning, my research focuses on one piece of that puzzle, i.e. trying to find an answer for one of those smaller problems: Do the surface properties that enhance bacterial attachment to chitin also enhance attachment to ordinary plastics surface and, if they do, is there a preference for a specific kind of material?