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Heat Wav: Plastic

In 2016, Japanese scientists discovered a bacterium that could eat PET, the type of plastic most water bottles are made of. In the final episode of our podcast, host Ellen Glover talks with two scientists who are trying to engineer an improved version of the bacteria’s enzymes that will consume plastic faster.

Ellen Glover Hello and welcome to Science Node podcast, an audio series that explores the ways big data and high performance computing are changing the world. Megabytes, gigabytes, terabytes, petabytes of data are being collected every day by researchers everywhere. In this podcast we break that down. We’re looking not only at the latest scientific discoveries, but the multi-billion dollar industry that’s backing them up. Literally. One of the hottest areas of research right now is climate change. Rising oceans, rising temperatures, rising piles of garbage...we’re covering it all in this four-part series. Welcome to the Heat Wav.

Ellen Glover There’s an island of garbage floating in the Pacific Ocean that’s twice the size of Texas. Much of this trash is plastic, specifically PET. 

Gregg Beckham PET is polyethylene terephthalate. 

Ellen Glover It’s the fourth most-produced plastic and it’s pretty versatile.

Lee Woodcock It is one of the most common plastics on the planet. 

Gregg Beckham It’s the plastic that goes into our water bottles and into our carpets. And it’s also the plastic that’s in our clothing, when we see polyester on our clothes tags.

Ellen Glover I spoke with researchers Gregg Beckham, a senior research fellow at the US National Renewable Energy Laboratory, and Lee Woodcock, a professor of chemistry at the University of South Florida, about the problems with PET plastics. We also discussed a possible solution to the mountains of plastic in our oceans and landfills. It’s a bacterium that eats PET as a major food source. We’re going to zoom out for a bit, though, so you can understand just how big this problem is. To start, the PET is too stable according to Woodcock.

Lee Woodcock We’ve made things that have tremendous properties for food storage and stability, but the problem is that, when they get discarded in irresponsible ways or incorrectly, they’re too stable and they just sit around in the environment for hundreds of years. Just taking up space and causing problems.

Ellen Glover Beckham, Woodcock’s colleague, says that, when these plastics do wind up in landfills and oceans, they’re estimated to take about 450 years to degrade naturally. 450 years ago, Elizabeth I and Mary Queen of Scots were fighting over England’s throne. The United States was still 200 years away from independence. Imagine how different our world will be when today’s plastics finally degrade. Although PET is the easiest plastic to recycle, only a small fraction of it even winds up in our recycling plants.

Gregg Beckham When you do recycle PET, typically it’s is down-cycling. You’re taking something that has excellent mechanical properties and mechanical strength—for example, a water bottle, which is PET—when you recycle it, it’s done mechanically and you reduce the material property such that, typically, it cannot be used as a water bottle again. 

Ellen Glover And it was at a water bottle recycling plant where the initial discovery of that plastic-eating bacterium was made.

Gregg Beckham In 2016, a group of Japanese researchers reported a very exciting discovery. They went out and dug in the soil around a Japanese PET bottle recycling plant and they were, in particular, looking for a bacterium that was able to eat PET as a major food source. And they found one that is able to degrade polyethylene terephthalate, or PET.

Lee Woodcock Through research and discovery, they determined that one of the key pieces of this was a couple of enzymes the bacteria have, that are unique, that facilitate breaking down these polyesters, or PET. Thus, it can be used for a carbon source or an energy source.

Gregg Beckham One of those enzymes, PET-ase, is actually able to attack the solid plastic and break that down into its building blocks. Then those building blocks, which are much smaller, the bacterium can eat as food.

Ellen Glover With that initial discovery, Woodcock, Beckham and a team of researchers coming from labs out of the UK, Colorado, Florida, and Brazil, wanted to better understand how this enzyme, called PET-ase, worked.

Gregg Beckham What we were interested in understanding was how did an enzyme in a bacterium evolve to be able to eat this manmade synthetic plastic? Obviously, PET hasn’t been around that long. We’ve only been making it at a large scale since the 1970s or so. And so our hypothesis was that this bacterium has evolved an enzyme, likely from some natural enzyme, that’s able to break down PET. 

Lee Woodcock Additionally, during that process, really as a way to try to figure out how this enzyme maybe has evolved from other closely related enzymes. We started playing with it, essentially, to try and see if we could turn it back into an enzyme that doesn’t break down plastics.

Ellen Glover However, instead of making the enzyme unable to break down plastic, they wound up making it even better. 

Gregg Beckham Why that’s exciting and why that’s interesting is, A) we don’t understand necessarily how these natural enzymes are evolving to be able to eat manmade plastics. I think even more exciting is what it tells us is now we have a foothold for using protein engineering and techniques that are tried and true and have been around in the scientific community for several decades now. To actually engineer an even better version of PET-ase, such that we could use it in industrial processes, we could make it much, much faster.

Ellen Glover To do this, the researchers used the National Science Foundation (NSF) XSEDE supercomputing facilities. Specifically, the machines at the Texas Advanced Computing Center, the San Diego Supercomputing Center and the National Renewable Energy Laboratory, to create simulations.

Gregg Beckham What we wanted to do was understand how the actual plastic, PET polymer, could bind to the enzyme. Most of the computer simulations that we did were trying to do high-fidelity docking calculations to understand how a small ligand that would look like a polymer, a PET, would stick and sit in the enzyme. What that allowed us to do was to explain why, when we made those genetic modifications to the enzyme, why we think we got a better variant of the enzyme itself. 

Lee Woodcock These facilities really offered us the ability that we didn’t have locally to be able to carry out some of the simulations that were able to predict some of these mutations and were able to rationalize why they could be stabilizing PET and thus enhancing the activity of the enzyme, especially after we made the mutations. For us, the facilities were absolutely necessary. I think in terms of the broad scientific community, it ranges. Some people have local resources where these facilities merely facilitate getting the research done faster. But there are a vast majority of people that don’t have access to the types of facilities like these to where the research couldn’t be done at all. And I think that’s probably more common--is that the research that goes on and is facilitated by having these XSEDE resources and having NSF sponsorship of these, couldn’t really be done in a large part without these facilities.

Ellen Glover Although the researchers know PET-ase breaks down these plastics faster than it would naturally, they aren’t quite sure by how much. The changes are easy to see when you look at just one plastic bottle. But the problem is so much bigger than that. Millions of tons of plastic are being produced every year and most of it’s winding up in landfills with some escaping into the environment. According to Beckham, we still don’t fully understand the ecological impacts of this, and many microorganisms are likely evolving to consume plastic. As for PET-ase, Woodcock says he and his team of researchers were able to speed it up by 30 percent with their modifications, and more work is being done to figure out ways to speed it up even more. It’ll be a while before this method leaves the lab and gets implemented industrially, though. 

Lee Woodcock I think it’s going to be a long time before they take over, or maybe not a long time, but an intermediate time before they can be used completely independent. But I see the day coming in the not too distant future where these are definitely going to play a role on the industrial scale.

Ellen Glover Woodcock says a couple of key things need to happen before PET-ase can be used in the real world.

Lee Woodcock We need to figure out how to stabilize the enzyme and we need to figure out how to make additional mutations to it to speed up the activity of it so we can break down the PET faster. There’s a couple of ways to do that, one is we continue to make modifications that will basically facilitate the breaking of these ester bonds. Another way is try to enhance it thermo-stability. Because, as you heat up plastic it becomes a lot more pliable and then easier to break down. The problem with that is that, if you want to use the enzyme to work on the heated plastic, the enzyme itself has to be able to withstand the heat. 

Gregg Beckham There’s a fun experiment you can do with a soda or a water bottle, a PET bottle. If you take it home and you boil some water on your stove and you put that bottle into the boiling water, you’ll see it turn into kind of a gooey mess. What you’re doing is your taking it above its so-called glass transition temperature, where it’s able to flow and you’ll get much more surface area. If we’re able to design industrial processes and of course find the enzymes that go along with them that are able to withstand high temperatures like that, we think we can dramatically accelerate the break-down of PET by these enzymes. 

Ellen Glover Reducing our plastic footprint has been at the forefront of the environmental protection conversation for a while now. Most recently, states like California and Alaska made headlines when they imposed strict bans on plastic straws and bags. Grocery store chain Kroger announced they would phase out plastic bags by the year 2025 in an effort to protect the planet. I was curious to know how the research community felt about that. Did they think this would be as effective? 

Gregg Beckham Certainly I advocate for as many solutions to be on the table and evaluated simultaneously as possible. There’s something like 40 percent of all plastics produced are used for packaging. Much of that is for single-use packaging. We’re making plastics that can withstand and last hundreds and, in some cases, thousands of years, that we’re using, in some cases, minutes to hours. Certainly I think that judicious redesign of plastics to be biodegradable, to be more easily recyclable, and certainly the push towards reducing our plastic use, has to be a major component of any judicious sort of pollution management. 

Lee Woodcock We have too much dependency on single use plastics right now and, no matter how efficient you get at recycling them, it’s never going to be enough to meet the demand of what the world is ramping up to. The demand for plastic has increased astronomically over the past few years, and I don’t see the demand getting any less. It’s only going to be by way of making conscious decisions to not do it is how we’re going to reduce that.

Ellen Glover Although this mountain of plastic appears looming, Woodcock and Beckham seem positive about the many solutions being developed, mainly because there is so much collaboration to get this work done.

Gregg Beckham The work that we’ve done so far and are continuing is really a multi-disciplinary and highly international collaborative effort. That shows that there’s a lot of excitement about this problem in the scientific community. I think there’s sort of a call to arms for scientists and engineers and researchers and social scientists as well to be thinking about how do we all attack this problem together. So I’m very excited about that.

Ellen Glover This episode of Heat Wav was brought to you by Science Node, an online magazine developed in collaboration with organizations in the US and Europe to bring information exploring the real-world impact of advanced computing and networks to experts and non-experts alike. Our featured sponsors today were XSEDE, the Texas Advanced Computing Center, and the San Diego Supercomputer Center. For more information about the project discussed today, visit pnas.orgdirect link will be on our website. Check out all of our Heat Wav episodes on Science Node’s website and keep an eye out for any further series. I’m your host, Ellen Glover. Thank you so much for listening.

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Music credits: “Memory” by Creo; “Driving Through Tunnels” by Daniel Birch; “Airliner” by Podington Bear; “Trying My Best To Move Forward” by Daniel Birch; “On the Clock” by Pictures of the Floating World; "Sullen Faced" by Kesta.

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