A diverse microbiome of bacteria and plastic-degrading fungi lives in salt marshes on the coast of Jiangsu, China.
It was identified by an international team of scientists who counted 55 bacterial and 184 fungal strains that are able to break down a biodegradable polyester called polycaprolactone (PCL), often used in polyurethane production, a press release from the Royal Botanic Gardens, Kew, said.
“The growing body of scientific evidence sheds light on the environmental potential for plastic degradation that needs to be unlocked,” Dr. Irina Druzhinina, senior research leader in Fungal Diversity and Systematics at Royal Botanic Gardens (RBG) Kew, told EcoWatch in an email. “Although plastic is a very new material, we possess some biochemical knowledge regarding the biological activities potentially involved in breaking down these polymers. We have observed that the genomes of fungi and bacteria encode promising enzymes that could contribute to plastic degradation.”
Of the bacterial strains identified, those within the genera Streptomyces and Jonesia may have the ability to further break down additional petroleum-based polymers — chains of synthetic or natural molecules bound together.
“Microbiologists across the board feel responsible for finding solutions to the ecologically friendly treatment of plastic waste because bacteria and fungi will be the first organisms to learn how to deal with this new material. We have no doubt that microbes will figure out ways to effectively degrade plastic, but this may take thousands of years if we leave nature to run its course,” Druzhinina said in the press release. “That is why our task is to utilise the knowledge we already possess of microbial biology, to speed up and direct the evolution of microbes and their individual genes to do the job now.”
The study, “The distinct plastisphere microbiome in the terrestrial-marine ecotone is a reservoir for putative degraders of petroleum-based polymers,” was published in the Journal of Hazardous Materials.
The scientists took samples of the plastic-degrading microorganisms from Dafeng, near China’s Yellow Sea Coast and a UNESCO-protected site, in May of 2021. A terrestrial plastisphere — a relatively new term to terrestrial ecology — was confirmed. The microbiome of the coastal plastic debris was also different from the soil that surrounded it.
“The initial exploration of microbial biofilms on plastic waste primarily focused on the marine environment. In our study, we chose to examine the marine-terrestrial ecotone (the borderline ecosystem) due to its unique characteristics, which make it somewhat reminiscent of the marine environment while being significantly richer in carbon and other nutrients. Delving into these highly diverse microbiomes was a bold decision, but it proved rewarding,” Druzhinina told EcoWatch. “Our sampling strategy deliberately avoided the most heavily polluted coastal areas. Instead, we aimed to observe the natural behavior of microbiomes in colonizing plastic debris. The DaFeng natural wetlands in Yancheng, included in the UNESCO World Heritage List, became our chosen location. This area is home to a diverse array of bird species, including the extremely rare Chinese crested-tern (Thalasseus bernsteini) with its distinctive yellow beak, as well as the stunning and endangered red-crowned cranes (Grus japonensis).”
The extent of the plastic pollution problem has steadily increased since the 1970s. Each year, 400 million tonnes of plastic waste is produced, according to the United Nations Environment Programme, and increasingly more often scientists are looking to bacteria, fungi and other microorganisms to help deal with it.
Thus far, 436 species of bacteria and fungi have been discovered that break down plastic. The scientists from Kew and their partners are hopeful that their latest discovery may lead to the designing of efficient enzymes to degrade plastic waste biologically.
A “microbial reef” for bacteria and fungi has been created by the plastics that have ended up in aquatic ecosystems because of their hydrophobic surface and longevity. And with some biodegradable plastics, microbes are provided with a carbon — or food — source.
Fifty plastic waste samples were collected by the researchers at Dafeng from seven types of petroleum-based polymers: polyurethane (PU), polypropylene (PP), polyvinyl chloride (PVC), expanded polystyrene (EPS), polyethylene terephthalate (PET), polyethylene (PE) and polyamide (PA).
The scientists identified 14 different genera of fungi, including plant pathogens Neocosmospora and Fusarium. Fungi that are plant pathogens get their nutrients from plants in a way that causes harm to their host. The findings of the study suggest that these fungi may be more adept at breaking down PCL plastics and other kinds of synthetic polymers than fungi that feed on dead organisms.
“The ecological niche of the Dafeng salt marshes is precisely why we chose to investigate the microbial communities present in the plastic waste there, and so far our findings have proven to be both exciting and promising,” Druzhinina said in the press release.
Fungi help break down organic matter in natural settings as part of the carbon cycle. They have evolved to break down complex natural polymers like cellulose over millions of years. The enzymes fungi secrete are adept at breaking down organic compounds like proteins and carbohydrates, which are complex.
“The ecological niche is not only a physical place where an organism lives but also its biotic and abiotic surroundings, including its habitat, available resources, stressors, and interactions with other species. Although many types of plastic debris possessing different properties are released into the environment, the ability of the plastic surface to repel water, the hydrophobicity, is the key parameter to understanding the development of plastisphere microbiomes,” Druzhinina told EcoWatch. “Furthermore, much plastic debris has an irregular and porous surface texture, expanding the total surface area and creating a diversity of microscale habitats that different microbes can colonize. It is also interesting to imagine a kind of chain reaction in the development of plastisphere microbiomes – the biofilm formed by the first colonizers, microbes capable of attachment to the specific surface, will attract microbial ‘grazers’ which will find it a valuable food resource compared to the surrounding environment. Thus, the plastisphere microbial community will grow and develop. So, in other words, the plastisphere microbiome is formed not by bacteria and fungi, which feed on plastic, but by the microbe capable of attaching to this unique surface.”
The researchers found two of the types of bacteria growing alongside the Dafeng fungi to be promising candidates for breaking down plastic — Streptomyces and the genus Jonesia, which was discovered recently. Jonesia cf. Quinghaiensis was especially dominant in the 55 bacterial strains that were sampled.
The authors of the study said that, despite the promising findings that are being made, humans’ understanding of plastic-associated microorganisms is just beginning, and there are still plenty of questions that remain unanswered; not all of the strains that were analyzed were able to be identified to a species level.
“What strikes me the most is the sheer power of microbial diversity, especially if you consider how challenging it is to detect them; they are microscopic in size, secretive in nature, and simple in appearance. However, when we shift our perspective and view them through a biochemical lens, we gain access to an abundant complexity that awaits our exploration,” said Dr. Feng Cai of Sun Yat-sen University in Shenzhen, China, in the press release. “It is truly exhilarating to realise we have barely scratched the surface and have already discovered a wealth of potentially promising resources for future technologies. This realisation fills me with an incredible sense of satisfaction, knowing that there are numerous discoveries still to be made and that our work can potentially lead to significant advancements in the field.”
More than 144,000 species in the fungi kingdom have been described to date, but many species — some scientists say several million — are yet to be discovered. One thing scientists agree on is that among these undiscovered species are new sources of medicine, food and other compounds that could benefit humans.
“[W]e and many other microbiologists worldwide aim to develop a technology for the efficient, inexpensive, and sustainable recycling of plastic waste; we do not target to eliminate this material. It will not be a single microbe that will solve the problem of plastic waste but an extensive technological framework with a multitude of options for tuning it to specific requirements and conditions,” Druzhinina told EcoWatch. “The development of plastic-degrading technologies follows a ‘yellow brick path’ that involves searching for microorganisms with genomes encoding potentially promising enzymes, employing computer modeling and artificial intelligence to improve these enzymes, producing the enzymes in suitable microbial cell factories, and implementing them in biotechnological pipelines. Our study provides the library of possible starting genomes, which are more likely to possess suitable genes for engineering. Although there is still a long way to go, we are committed to expediting the process.”
Druzhinina told EcoWatch that it was not foreseeable for plastic-eating fungi to be used to break down existing plastic in the environment, like the Great Pacific Garbage Patch.
“Even if such microbes were engineered, using genetically modified organisms (GMOs) or deliberately introducing non-native organisms into ecosystems raises regulatory and safety concerns in many countries. Strict regulations and guidelines are likely to be in place to ensure that any proposed interventions are rigorously tested, safe, and comply with environmental protection standards. The Great Pacific Garbage Patch should likely be recycled in a controlled setting based on a technology which should be developed for it. It is still a long way to go,” Druzhinina said.
Druzhinina added that it was foreseeable for plastic-eating fungi to be used to break down commercial plastic waste that ends up in landfills or that is put into recycling receptacles but not actually broken down and reused.
“Yes, we expect the development of technology for the efficient recycling of commercial and household plastic waste. Unfortunately, the only way to biologically degrade plastic debris, which has already been released into the environment, is to collect them and bring them to the respective (future) plastic waste treatment plants,” Druzhinina told EcoWatch. “Likely, the gradual decline of petroleum resources for making new plastics may force the development of technologies to collect and reuse plastic from the environment. We live in the Plastic Age with all its benefits and challenges.”
Druzhinina offered advice for individuals who want to help mitigate the world’s plastic problem.
“Join us on this ‘yellow brick path’! Engage in research, explore microbes, promote biodiversity conservation programs, and study chemistry, biology, and math. There are many things to be done: invent biodegradable alternatives to plastics, develop AI technologies for picking up the best genes, and model enzyme activity on plastics… The progress in all areas of modern science will speed up the technology development to combat the plastic waste problem and other challenges,” Druzhinina said. “I also encourage society to talk about this issue… Fortunately, the quest for plastic-degrading microorganisms and genes has become the forefront of modern microbiology, and we take great pride in being part of this endeavor.”
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