Thriving in the “Plastisphere,” Plastic-Eating Fungi Offer Hope in Tackling Global Waste Crisis

A new study published in Hazardous Substances Journal Researchers at the Royal Botanic Gardens, Kew and associates have identified a diverse microbiome of plastic-degrading fungi and bacteria in coastal salt marshes in Jiangsu, China.

The international team of scientists counted a total of 184 fungal strains and 55 bacterial strains capable of breaking down polycaprolactone (PCL), a biodegradable polyester commonly used in the production of various polyurethanes. Among these bacterial strains within the genus Gonzia and Streptomyces have the ability to further degrade other petroleum polymers—natural or synthetic chains of molecules linked together.

Samples of plastic-degrading microorganisms were taken in May 2021 from Dafeng in eastern China, a UNESCO-protected site near the Yellow Sea coast. Sampling confirmed the presence of a terrestrial blastosphere, a relatively new term in terrestrial ecology as previous studies have focused primarily on marine environments. The microbiome in this “man-made ecolodge” of coastal plastic debris was found to be distinct from the surrounding soil.

Scientists are increasingly looking at microorganisms, such as fungi and bacteria, to help tackle some of the most pressing challenges of modern times, including the rising tide of plastic pollution. According to the United Nations Environment Program (UNEP), 400 million tons of plastic waste is generated annually, with plastic pollution levels increasing sharply since the 1970s. However, researchers hope to find answers to this problem in the plaspheres.

Previous research has already recognized the ability of microorganisms to process plastic waste; A 2017 study led by researchers from China and Pakistan identified a strain of the fungus Aspergillus tubingensis that was breaking down plastic at a landfill in Islamabad, Pakistan. To date, 436 species of fungi and bacteria have been found to degrade plastic and Kew scientists and partners believe their latest findings could lead to the development of efficient enzymes designed to biodegrade plastic waste.

The research arrives ahead of World Environment Day 2023 on June 5, with the theme of finding solutions to the plastic waste crisis as part of the #BeatPlasticPollution campaign.

“Microbiologists across the board feel a responsibility to find solutions for environmentally friendly handling of plastic waste because bacteria and fungi will be the first organisms to learn how to handle this new material,” says Dr. Irina Druzhinina, Senior Researcher in Fungal Diversity and Systematics at RBG Kew. “I doubt that microbes will figure out ways to effectively degrade plastic, but that could take thousands of years if we let nature take its course. That’s why our mission is to take advantage of the knowledge we already have of microbial biology, to accelerate and direct the evolution of microbes and their individual genes to do the job now.”

Because of their longevity and waterproof surface, plastics in aquatic ecosystems have created “microbial reefs” of sorts that fungi and bacteria adhere to. And in the case of some biodegradable plastics, it can provide microbes with a source of carbon for metabolism — a food source. In Dafeng, researchers collected 50 plastic waste samples from seven different types of petroleum polymers: polyethylene terephthalate (PET), expanded polystyrene (EPS), polyethylene (PE), polyurethane (PU), polyamide (PA) and polypropylene (PP), and polyvinyl chloride (PVC).

Among the samples, the researchers identified 14 genera of fungi, including the plant pathogens Fusarium and Neocosmospora. Phytopathogenic fungi derive their nutrients from plants but do so in a way that is detrimental to their host. The results of the study suggest that these fungi may be better at degrading PCL plastics and other synthetic polymers than mycorrhiza fungi — fungi that feed on the remains of dead plants and animals.

Dr Druzhinina adds: “The ecological status of the Dafeng salt marshes is precisely why we chose to examine the microbial communities found in plastic waste there, and so far our findings have proven exciting and promising.”

In the wild, fungi play a major role in breaking down organic matter and transporting it through the carbon cycle. Over millions of years, the ability to break down many complex and naturally occurring polymers, such as cellulose, has evolved. In fact, the enzymes secreted by fungi are very effective at breaking down complex organic compounds, including carbohydrates and proteins.

Besides Dafeng fungi, the research team identified two genera of bacteria, Streptomyces and the recently discovered genus Jonesia, as promising candidates for plastic degradation. In particular, the species Jonesia cf. Quinghaiensis dominated 55 bacterial strains taken.

Xuesong Li, a Masters student at Nanjing Agricultural University, China, says, “The opportunity to work on a project with potentially impactful solutions to address the increasing levels of plastic pollution worldwide was an immediate draw, especially since this was my first research project. It was There is some initial concern that we may not be collecting enough data from a single sample, but the results so far have been overwhelming, and we have had to restrain ourselves from isolating more and more cultures to study their properties.Although the bacteria proved highly active in this regard, I personally preferred Working with fungi, these organisms have huge potential for applications far beyond plastic degradation.”

Despite the many exciting advances in this field, the study authors caution that our understanding of plastic-associated microorganisms is still in its infancy. Many questions about these ecological niches remain unanswered and the study authors encountered some limitations in accurately identifying the analyzed lineages down to the species level.

Dr Feng Kai, of Sun Yat-sen University in Shenzhen, China, says, “What amazes me most is the sheer power of microbial diversity, especially if you consider how hard it is to detect them; they are microscopic in size and secretive in nature, and simple in appearance. However, when we change Our perspective and looking at them through a biochemical lens, we gain access to a bountiful complexity that awaits our exploration.It is really gratifying to realize that we have barely scratched the surface and that we have already discovered a wealth of potentially promising resources for future technologies.This realization fills me with an incredible sense of satisfaction , knowing that there are many discoveries still to be made and that our work can lead to significant advances in this field.”

RBG Kew is home to one of the world’s oldest and largest fungi with over 1.25 million specimens, but the kingdom of fungi remains one of the natural world’s biggest mysteries. Estimates vary but there may be several million species yet to be discovered on top of the more than 144,000 species described so far, and scientists stress that among them are new sources of food, medicine and other beneficial compounds.