In 2001, a group of Japanese scientists made a remarkable discovery at a landfill site: nestled amidst layers of dirt and discarded items, they stumbled upon a peculiar find. A slimy film of bacteria was thriving, actively breaking down plastic bottles, toys, and assorted refuse. These microorganisms were, in essence, “eating” plastic by converting it into energy, propelling their growth and reproduction. While their consumption of plastic differed from the way we typically understand eating, there was no denying that these bacteria were indeed consuming plastic.
Leading this team of scientists was Professor Kohei Oda from the Kyoto Institute of Technology. Oda, a microbiologist, held a profound belief that nature often held the solutions to complex scientific problems. He urged people to observe nature closely, as it often offered ingenious solutions to a myriad of challenges.
What Oda and his colleagues uncovered was nothing short of revolutionary. Initially, they were hoping to find microorganisms with rudimentary methods to attack plastic surfaces. However, the bacteria they discovered were far more sophisticated—they were breaking down plastic materials completely, converting them into essential nutrients. In the context of our current awareness of plastic pollution, the significance of this discovery is evident. However, back in 2001, several years before the term “microplastic” became common parlance, this finding generated relatively little interest.
Conquering plastic pollution
Fast forward to today, and plastic pollution has reached unprecedented levels. In the span of roughly two decades since the discovery of these plastic-consuming bacteria, the world has generated a staggering 2.5 billion tonnes of plastic waste, with an additional 380 million tonnes produced annually. Projections indicate that this figure may triple by 2060. Oceans are marred by patches of plastic debris, some spanning areas seven times the size of Great Britain. Plastic waste chokes beaches and inundates landfills across the globe. Even more alarmingly, microplastic and nanoplastic particles have infiltrated fruits, vegetables, and have been discovered lodged in nearly every human organ, including breast milk.
The current methods employed for breaking down or recycling plastics are woefully inadequate. Conventional plastic recycling largely entails crushing and grinding, a process that damages the plastic fibres, resulting in lower-quality materials. In stark contrast to materials like glass or aluminium, plastic degrades with each recycling cycle. Furthermore, a mere 9% of plastic waste finds its way into recycling plants, and incineration is often the ultimate fate for much of it. Incineration, while a disposal method, exacerbates the climate crisis by releasing carbon and potentially hazardous chemicals into the atmosphere.
In the years following their initial discovery, Professor Oda and his student-turned-professor, Kazumi Hiraga, continued their correspondence and experiments. Eventually, in 2016, they published their work in the prestigious journal Science. Their discovery, the bacterium Ideonella sakaiensis, capable of breaking down polyethylene terephthalate (PET), the most common plastic found in clothing and packaging, catapulted them into the limelight. The publication garnered widespread attention and now boasts over 1,000 scientific citations, placing it among the top 0.1% of all scientific papers.
The true power of bacteria
However, the real promise lies in the broader realm of microbiology. Over the past half-century, microbiology, the study of small organisms such as bacteria and some fungi, has undergone a remarkable transformation. Former President of the American Society for Microbiology, Jo Handelsman, described it as possibly the most significant biological advance since Charles Darwin’s groundbreaking work on evolution. We now comprehend that microorganisms constitute a vast, hidden world intricately intertwined with our own. Scientists have only begun to scratch the surface of their diversity and astonishing capabilities. Many scientists, like Professor Oda, now share the belief that these microorganisms may already hold solutions to a host of seemingly intractable problems. The key is to look to nature for inspiration.
Yet, a discovery like Professor Oda’s is merely the starting point. To have a substantial impact on the colossal environmental disaster that plastic pollution represents, these bacteria must work faster and more efficiently. In initial lab tests, Professor Oda’s team placed the bacteria alongside a small piece of plastic film and observed it breaking down into precursor liquids over approximately seven weeks. While this was impressive, it remained far too slow to make a meaningful dent in plastic waste at a global scale.
Engineering the enzymes
Fortunately, in recent decades, scientists have become increasingly proficient at manipulating and engineering enzymes, which are integral to the breakdown of larger compounds, including plastic. Enzymes facilitate chemical reactions at a microscopic scale, making them ideal candidates for enhancing the plastic decomposition process. Scientists can modify the DNA that encodes enzymes, altering their structure and function to improve stability and effectiveness.
However, there are limitations to this process. Designing enzymes logically doesn’t always lead to the desired outcome, and predicting the specific modifications that will enhance their performance remains challenging. Elizabeth Bell, a researcher at the US government’s National Renewable Energy Laboratory, emphasizes the complexity of this task. Her work focuses on PETase, the enzyme that Ideonella sakaiensis produces to break down PET plastics. To expedite progress, Bell employs a brute-force approach, subjecting enzyme regions that directly target plastic to countless mutations through genetic engineering. This approach generates numerous potential mutants, which are then evaluated for their plastic-degrading capabilities. Those showing even marginal improvement undergo further rounds of mutations. This method has already led to the development of enzymes capable of degrading PET much faster than the original enzyme.
Could the answer lie in nature?
Creating enzymes that align with human purposes, however, is not a straightforward process. Before Professor Oda’s groundbreaking publication in 2016, no one knew that bacteria capable of digesting plastic existed. While we now have evidence of one such bacterium, Ideonella sakaiensis, the microbial world remains vastly unexplored. As a result, we may be attempting to extract elite performance from an organism equivalent to a Toyota Yaris engine, while an undiscovered bacterial equivalent of a Ferrari could exist elsewhere. This dilemma poses a critical question: should we continue searching for nature’s solutions or focus on laboratory-based research to engineer optimal enzymes?
The quest for plastic-consuming microbes has led to bioprospecting, a practice where scientists venture to diverse and often extreme environments across the globe in search of valuable microorganisms. From municipal dumps in South Korea to the brackish waters of mangrove swamps in Vietnam and Thailand, researchers are on an expedition to uncover new plastic-eating organisms.
In hindsight, microbes were once overlooked and underestimated. They were often considered mere pathogens or rudimentary industrial tools. However, the field of microbiology has evolved significantly. Thanks to advances in DNA sequencing and other biotechnological methods, we now possess a deeper understanding of the staggering genetic diversity of microorganisms. This newfound knowledge has illuminated their potential applications and ecological roles.
One of the fascinating attributes of microbes is their adaptability. These microorganisms evolve at a rapid pace, thriving in extreme and diverse environments. This adaptability positions them as ideal candidates to tackle contemporary challenges, including plastic pollution. As Professor Oda eloquently suggested, these microorganisms may indeed hold answers to problems of our own making.
Future unclear
However, the path forward is not without its challenges. The legal and environmental risks associated with releasing genetically engineered microbes into the wild are considerable. Striking a balance between innovation and caution is of paramount importance as we pursue microbial solutions to combat plastic pollution.
The potential of microbes to address the global plastic pollution crisis is a promising avenue of research and innovation. While there have been significant breakthroughs and discoveries, many challenges remain to be overcome. Scientists continue their tireless quest to harness the extraordinary power of these tiny organisms in a bid to mitigate one of humanity’s most pressing environmental challenges. The story of these plastic-eating bacteria is emblematic of humanity’s ongoing journey to reconcile our technological advancements with the natural world, reminding us that solutions may often be found where we least expect them—in the realm of the microscopic and the microbial.
