The global plastic pollution crisis surge has led to a relentless search for new strategies that could reduce plastics’ detrimental impacts on the environment. According to Our World in Data, an online publication for global problems, the production of plastic has increased significantly in the past seventy years. In 1950, global plastic production was two million tonnes, but it has now increased to over 450 million tonnes. 

Plastic debris in the environment can cause a significant threat because it does not decompose quickly compared to other materials. It resists natural processes like sunlight exposure, heat, physical forces, and even microorganisms, allowing it to persist in ecosystems for long periods.

Traditional waste management methods such as recycling and incineration have been futile in reducing the amount of plastic in the world, creating a need for novel directions. Scientists are delving into the fascinating world of fungi to learn what power these species wield to degrade plastics and potentially revolutionize how they impact our world.

Fungal diversity and role in ecosystems

Fungi are a diverse group of microorganisms — consisting of approximately 144,000 known species. They’re one of the most widely distributed organisms on Earth. While many fungi independently reside in soil or water, others establish parasitic or symbiotic relationships with plants or animals. 

In a symbiotic relationship, fungi and bacteria work in tandem to disintegrate organic matter, releasing carbon, oxygen, nitrogen, and phosphorus into the soil and atmosphere. Fungi have demonstrated an impressive ability to break down synthetic materials — such as plastics — proposing a sustainable and environmentally friendly strategy to combat the large amounts of plastics in our environment. 

Fungal enzymes: Plastic’s doom

Synthetic plastics are hydrophobic, non-biodegradable large molecules — or polymers — consisting mainly of crude oil. Fungi has one of the most efficient microbial biodegradation of plastic polymers, which means they can break down plastic. In the presence of optimal environmental factors, fungi grow on the surface of the plastic, leading to the secretion of extracellular enzymes like hydrolases and oxidoreductases, which will degrade the plastic. 

The polymers’ hydrophilic — or water-loving — properties relate to the substance’s ability to attract and engage with water. The hydrolase enzymes enhance the water-attracting traits of polymers, while the oxidoreductases break down the polymers into smaller particles, which allow them to pass through the fungal cellular membrane. 

The process’s effectiveness increases when biodegradation occurs after the plastic breaks down due to interactions with light and heat. Fungi’s innate ability to decompose organic matter has positioned them as integral contributors to industries like pharmaceuticals and food and beverage production.

Tapping into fungal potential

A recent publication in the journal Science of the Environment investigated the potential ways fungi can be employed for their bio-remedial effects — the use of microbial species to decontaminate physical environments — in the context of plastic and rubber waste. Specifically, the study focused on identifying fungal strains capable of degrading three common synthetic plastic types: polyurethanes, polyethylene, and tire microplastics. 

Researchers aimed to pinpoint the mechanisms involved in fungal plastic degradation and determine the factors influencing the plastic decomposition rate and efficiency. After isolating and identifying 18 fungal strains using molecular sequencing — a laboratory process that involves the determination of the exact species using their DNA — researchers observed and measured the fungal strain’s ability to degrade as a function of oxygen consumption, carbon dioxide production, and changes in fungal biomass. 

Researchers used infrared spectroscopy — which measures how matter such as fungi and plastic absorb, emit, or reflect infrared radiation — to better understand changes in fungal growth across different plastic types and conditions. Then, researchers looked to see how strongly a certain strain of fungal biomass and dissolved plastic. 

The study revealed that all 18 strains grew on plastic particles, but only 11 of the 18 fungal strains showed ligninase activity, which is crucial for breaking down complex polymers. Respiratory assays — tests conducted to measure the metabolic activity of cells, organisms, or tissues by monitoring their oxygen consumption or carbon dioxide production — revealed that fungi degraded polyurethane the most effectively, with the Fusarium tricinctum and Penicillium crustosum species being the most active during the first two weeks of incubation, consuming 98.6 per cent and 94.2 per cent of the oxygen, respectively. This innovative exploration represents a leap forward to a transformative solution for the plastic pollution crisis and a more sustainable future. 

A promising future for fungal biodegradation

Despite the recent success in mycology, there remain considerable gaps in our understanding of the fungal biodegradation process. 

Further research must address limitations, including the restricted number of plastic polymers studied under controlled laboratory conditions, which may not accurately replicate real world environmental factors or their effect on fungal biodegradation rates. Long-term experiments are crucial to assessing the long-term effectiveness of fungal biodegradation in natural settings and identifying any potential negative environmental impacts, such as the release of toxic byproducts. 

Despite these limitations, exploring the biodegradation potential of fungi presents an opportunity to innovate sustainable plastic waste management strategies. Future directions can include improving fungi’s biodegradation capabilities through genetic modification and integrating synergistic approaches, combining fungal biodegradation with other waste management tactics for more holistic outcomes. 

Understanding fungi’s capabilities can positively contribute to developing practical and sustainable methods for plastic waste management and influence the research and applications of plastic-degrading fungi to inform global and local sustainable practices better.