A few years ago, an image of a vast mass of plastic floating in the Pacific ocean went viral alarming us about the gravity of the plastic waste problem we humans were creating:
To get the enormity of the situation, in the last 20yrs, “we have generated 2.5bn tonnes of plastic waste and each year we produce about 380 million tonnes more, with that amount projected to triple again by 2060. A patch of plastic rubbish seven times the size of Great Britain sits in the middle of the Pacific Ocean, and plastic waste chokes beaches and overspills landfills across the world. At the miniature scale, microplastic and nanoplastic particles have been found in fruits and vegetables, having passed into them through the plants’ roots. And they have been found lodged in nearly every human organ – they can even pass from mother to child through breast milk.”
Fortunately, there seems to be solution. Japanese scientists have discovered a species of bacteria which ‘eats’ plastic for its energy source.
“The scientists were led by Kohei Oda, a professor at the Kyoto Institute of Technology. His team was looking for substances that could soften synthetic fabrics, such as polyester, which is made from the same kind of plastic used in most beverage bottles. Oda is a microbiologist, and he believes that whatever scientific problem one faces, microbes have probably already worked out a solution. “I say to people, watch this part of nature very carefully. It often has very good ideas,” Oda told me recently.”
What Oda and his colleagues found in that rubbish dump had never been seen before. They had hoped to discover some micro-organism that had evolved a simple way to attack the surface of plastic. But these bacteria were doing much more than that – they appeared to be breaking down plastic fully and processing it into basic nutrients.”
Although the discovery was made as early as 2001, the scientists never published their research until 2016 as the gravity of the plastic waste situation rose:
“…in the paper, they described a specific enzyme that the bacterium was producing, which allowed it to break down polyethylene terephthalate (PET), the most common plastic found in clothing and packaging. The paper was reported widely in the press, and it currently has more than 1,000 scientific citations, placing it in the top 0.1% of all papers.”
How does this actually work?
“When any living organism wishes to break down a larger compound – whether a string of DNA, or a complex sugar, or plastic – they turn to enzymes, tiny molecular machines within a cell, specialised for that task. Enzymes work by helping chemical reactions happen at a microscopic scale, sometimes forcing reactive atoms closer together to bind them, or twisting complex molecules at specific points to make them weaker and more likely to break apart.
If you want to improve natural enzyme performance, there are approaches that work in almost every case. Chemical reactions tend to work better at higher temperatures, for instance (this is why, if you want to make a cake, it is better to set the oven at 180C rather than 50C); but most enzymes are most stable at the ambient temperature of the organism they work in – 37C in the case of humans. By rewriting the DNA that codes an enzyme, scientists can tweak its structure and function, making it more stable at higher temperatures, say, which helps it work faster.”
Other scientists such as Elizabeth Bell, a researcher at the US government’s National Renewable Energy Laboratory (NREL) in Colorado have picked up the baton to take this research forward:
“Bell takes the regions of the enzyme that work directly on plastic and uses genetic engineering to subject them to every possible mutation. In the wild, a mutation in an enzyme might occur only once in every few thousand times the bacteria divide. Bell ensures she gets hundreds, or thousands of potentially beneficial mutants to test. She then measures each one for its ability to degrade plastic. Any candidates that show even marginal improvement get another round of mutations. The head of the NREL research group, Gregg Beckham, refers to it as “evolving the crap out of an enzyme”. Last year, she published her latest findings, on a PETase enzyme she had engineered that could degrade PET many times faster than the original enzyme.”
Now scientists are on the look out for other species of bacteria that might be more powerful in breaking down plastic waste faster:
“This question has led to a boom in what is known as bioprospecting. Like panning for gold in a river, bioprospectors travel the world looking to discover interesting and potentially lucrative microbes. In 2019, a team at Gwangju National University in South Korea took a construction drilling rig to the municipal dump outside town, and drilled 15 metres under the trash trenches to reveal decades-old plastic garbage. In it, Prof Soo-Jin Yeom and her students found a variety of the bacterium Bacillus thuringiensis that appeared to be able to survive using polyethylene bags as food. Yeom’s team is now studying which enzymes the bacterium might be using, and whether it is really able to metabolise the plastic.”
The article elaborates the history of microbiology which has helped us understand the evolutionary science of bacteria:
“Their adaptability makes microbes the ideal companion for our turbulent times. Microbes evolve in ways and at speeds that would have shocked Darwin and his contemporaries. Partly because they divide quickly and can have population sizes in the billions, and partly because they often have access to evolutionary tricks unknown to more complex lifeforms – rapidly swapping DNA between individuals, for instance – they have found ways to thrive in extreme environments. And, at this historical moment, humans are creating more extreme environments across the globe at an alarming rate. Where other animals and plants have no hope of evolving a solution quickly enough to outpace their changing habitats, microbes are adapting fast. They bloom in acidified water, and are discovered chewing up some of the putrid chemicals we slough off into the natural world. Just as Kohei Oda suggested, for many of our self-created problems, they are proposing their own solutions.”
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