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The use of fungi in the removal of microplastics

  • March 11, 2024
  • 6 min read
The use of fungi in the removal of microplastics

Could our problem with plastics have a solution in nature? Plastics, a resource of modern invention, have only been a part of our world for just over a century. Yet, in this short time span, this highly versatile material has shaped our modern lives. From the 30 million tonnes produced in 1988, the annual plastic output skyrocketed to a staggering 359 million tonnes by 2018, with projections hinting at a tripling of this figure by 2060.

The story of plastic’s impact doesn’t end with its production boom. In the 1970s, the first inklings of trouble emerged as small plastic fragments surfaced in our seas. However, it wasn’t until 2004 that the term ‘microplastics,’ was coined, describing fragments measuring up to 5mm in diameter. Nanoparticles are even smaller at less than 1000 nm in size, which slip through filtration systems in sewage and wastewater treatment plants, adding another layer to the problem.

These resilient particles can be found in a wide range of surprising locations, from fields, oceans, rivers, and mountaintops, and are known to float around in the Earth’s atmosphere.

The problem with plastics is that they drift through the air we breathe, seep into the soil our crops grow in, and have even found their way into our bodies, detected in human breast milk and lurking within our organs. The concerning possibility of microplastics breaching the blood-brain barrier has spurred ongoing studies, raising questions about potential links to neurological disorders.

The pervasiveness of these minuscule pollutants underscores the urgency of finding solutions. But nature, it seems, might hold the key to remedying the mess we’ve made.

According to a recently published report by The Rivers Trust – The State of our Rivers – even the clearest-looking waters in the UK can contain microplastics, industrial chemicals, hydrocarbons, fertilisers, and pesticides, and even pharmaceuticals.

For the past two decades, science has been looking to nature to find a cost-effective and eco-friendly solution. Micro-organisms, such as fungi, bacteria, and algae, can biodegrade microplastics via a complex physio-chemical transformation of polymers into smaller units. By tapping into the natural mechanisms of these microorganisms, researchers are unlocking innovative solutions to combat microplastic pollution and mitigate its detrimental impacts on aquatic ecosystems.

Just over a decade ago, Yale made headlines with the discovery of a fungus in Ecuador, Pestalotiopsis microspora, that has the ability to digest and break down polyurethane plastic, even in an air-free (anaerobic) environment—which might even make it effective at the bottom of landfills. This process came to be known as mycoremediation. Fungi are adaptable organisms and can thrive in diverse environments. Researchers are exploring how different types of fungi can be harnessed to target specific types of microplastics, depending on the environmental conditions and types of plastics present. Peter McCoy, a self-taught mycologist and author of Radical Mycology, was able to “train” Pleurotus mycelium to digest used cigarette butts by phasing out other food alternatives. Over time, this fungus “learned” how to digest them, giving rise to its fruiting body, the oyster mushroom. This may be due to DNA encoding the necessary enzymes that have laid dormant for generations, only to be activated out of necessity.

Alternatively, it might involve an enzyme destined for something else that was repurposed. There are many nonspecific fungal enzymes, such as lignin peroxidases, that can allow the fungus to metabolise different compounds with similar structures. The Victorian government of Australia will be utilising this technique to condition the humble oyster mushroom to break down toxins and microplastics in up to 1.2 million butts that have been diverted from landfill. If this proves successful, it will no doubt inspire other governments and organisations to follow suit. Over the last few decades, the development of environmental DNA analysis and sequencing techniques has allowed scientists to identify all species in a given area by their individual genetic sequence. This has led to the discovery of nearly 2000 new species of marine fungi, most of which are microscopic.

There is still a great deal that is unknown about these fungi, but given their incredible resilience and adaptability at surviving the salinity and high pressures beneath the sea, they could offer us undiscovered waste management solutions. Fungi have been found living among the Great Pacific Garbage Patch, using the plastics as a food source. By pretreating these microplastics with chemicals such as nitric acid and sodium hydroxide, the rate of biodegradation can be accelerated for some species of fungi on certain types of plastics.

Microscopic algae are known to colonise the plastic surfaces in wastewater streams. These microalgae produce enzymes and toxins that could serve as effective microplastic degraders. Some have been made into genetically modified microalgal cell factories, which are capable of producing and secreting enzymes required for plastic degradation. In the future, we may see more genetically enhanced micro-organisms that can effectively get the job done with minimal harm to the environment.

Bacteria can work in a similar way, producing enzymes that catalyse microplastic breakdown. Scientists have genetically engineered a microorganism from two bacteria to break down polyethylene terephthalate (PET), a plastic used in everything from water bottles to clothing that is a significant contributor to microplastic pollution in oceans. The first, Vibrio natriegens, thrives in saltwater and reproduces very quickly. The second bacterium, Ideonella sakaiensis, produces enzymes that allow it to break down PET and eat it. The resulting microorganism expressed both these traits.

Given the complexity and pervasiveness of plastic pollution, elimination of microplastics from our ecosystems will require a combination of approaches. Bioremediation, bioengineered organisms, nanotechnologies, and chemical solutions will all be required. Biodegradable alternatives are not a fool-proof solution. They have a slightly lower fossil fuel footprint than conventional plastics but can still take years to break down and need controlled industrial conditions to do so completely.

Even if effective new solutions to tackling the problem with plastics are developed, we still have the issue of reducing the volumes of new plastic being produced. Currently, it is estimated only around 10% of plastic is recycled globally. This is, in part, due to the thousands of chemicals that give it its diverse properties, making it impossible to remix. If we are to make an impact on plastic pollution, then considerations must be made at the design phase, looking at minimising the use of plastic, looking at alternative eco-friendly and low-carbon materials, and ensuring products can truly and easily be recycled. This is a huge feat that can only be accomplished by a coordinated effort of governments, organisations, industry, and academia.

About Author

Natalie Shanahan

Natalie Shanahan has a BSc in Genetics and a MSc in Bioinformatics. She worked as a lecturer, teaching genetics and biochemistry, before moving to Australia to work for their first Bioinformatics company. Here she managed their marketing as well as working on their numerous educational resources. Natalie left her career in science to follow her passion and now works as a personal trainer and nutrition consultant, helping individuals and employees of large organisations, better understand their health and wellbeing.

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