NATURE PODCAST

Podcast: A plastic-recycling enzyme, and supercooled molecules

Hear about the latest science, with Nick Howe and Shamini Bundell.

This week, a new enzyme speeds up the breakdown of plastic bottles, and a method to cool molecules to a fraction above absolute zero.

In this episode:

01:18 A PET recycling enzyme

Researchers have engineered an enzyme that effectively breaks down the plastic PET into its constituent monomers. This could allow for more complete recycling of bottles and clothes. Research Article: Tournier et al.

06:41 Research Highlights

The shocking lengths humans will go to to satisfy their curiosity, and the reasons for elevated methane emissions at Oktoberfest. Research Highlight: Humans opt to brave electric shock to satisfy their curiosity; Research Highlight: Munich’s Oktoberfest is a real gas

09:15 Supercool molecules

Researchers have used a technique called ‘collision cooling’ to chill molecules to a few millionths of a degree above absolute zero, which could allow observations of difficult-to-study quantum mechanics. Research Article: Son et al.

14:46 Research Highlights

Neither supermassive, nor super small, the mystery of the elusive intermediate sized black-hole has been solved. Research Highlight: Elusive middle-weight black hole is caught shredding a star

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Transcript

This week, a new enzyme speeds up the breakdown of plastic bottles, and a method to cool molecules to a fraction above absolute zero.

Host: Nick Howe

Welcome back to the Nature Podcast. This week, supercool molecules…

Host: Shamini Bundell

And an efficient plastic-degrading enzyme. I’m Shamini Bundell.

Host: Nick Howe

And I’m Nick Howe.

[Jingle]

Host: Nick Howe

As you probably know by now, we’ve been making some changes recently, including recording from a variety of pillow fort studios in our living rooms and keeping the main Nature Podcast a coronavirus-free zone. I will just do a little plug, though, for our Friday Coronapod, where we’ve jammed in all the coronavirus science in one handy weekly show. Do check it out.

Host: Shamini Bundell

In the meantime, we’ve got plenty of fascinating science nuggets for you here, and starting us off, a better way to deal with plastic waste.

Host: Nick Howe

That’s right. I don’t think many people would argue with the importance of recycling plastic, but the way it’s currently done means that a lot of plastic actually ends up in landfill anyway. But this week in Nature, French company Carbios, working with the Toulouse Biotechnology Institute, report a powerful new way to avoid the landfill, using an enzyme to very effectively break down plastic. So, reporter Ali Jennings has been talking to Carbios’ chief scientific officer, Alain Marty. Ali started by asking Alain about the scale of the problem they set out to tackle.

Interviewee: Alain Marty

The problem is really plastic waste, and unfortunately, 9 million tons of plastics end up inside oceans each year. I think now it is no more acceptable for society and for consumer.

Interviewer: Ali Jennings

So, what kind of plastic did you focus on?

Interviewee: Alain Marty

Yes, PET – polyethylene terephthalate. It is one of the main polymers used, and it is the most abundant polyester. It is produced at 70 million tons annually in the world, and around 25 million tons are used in bottles and packaging and 50 million tons in textiles.

Interviewer: Ali Jennings

So, how do you deal with that much PET?

Interviewee: Alain Marty

The idea was to use enzymes to break down the polyester. To make PET, we have two monomers, and these two monomers are linked by an ester bond. And the enzyme is like molecular scissor, which will break this ester bond and liberate the two monomers.

Interviewer: Ali Jennings

So, is this enzyme fundamentally different or is it like the existing enzymes that are out there?

Interviewee: Alain Marty

We optimised the thermostability of the enzymes and we increased the performance of the scissors. We redesigned entirely the active site of this enzyme and at the end, the best results we obtained using post-consumer waste is to convert 90% of the PET into monomers in less than 10 hours.

Interviewer: Ali Jennings

And is that good compared to other existing techniques?

Interviewee: Alain Marty

If we compare with the best enzymes described so far in the literature, the performance of this enzyme is 100 times higher.

Interviewer: Ali Jennings

So, how did you feel when you first saw the results of what the enzyme could do?

Interviewee: Alain Marty

To be honest, I am always wondering how is it possible to obtain this kind of performance with a plastic. When we obtained this very, very good result, we were really very proud.

Interviewer: Ali Jennings

And how easy is it or how easy would it be to put this method into wider usage?

Interviewee: Alain Marty

It will only require the addition of a depolymerization unit to create PET in a normal PET production plant.

Interviewer: Ali Jennings

So, what you’re suggesting is that instead of going to a separate recycling facility, you would add this new block to an existing plastic production facility.

Interviewee: Alain Marty

Exactly, instead of using fossil-based resources to produce PET, the producer will be able to use plastic waste as the raw material, and they will produce the equivalent virgin PET. And we have already produced the first PET bottles we made with 100% recycled plastic, and our plan now is to construct an industrial demonstration plant where we will start the operation mid-2021.

Interviewer: Ali Jennings

So, what are the kind of consumer goods that we might expect to be able to give back to plastic manufacturers to turn into something else?

Interviewee: Alain Marty

It could be water bottles or soda bottles or shampoo bottles. It could be also packaging. But the main part is also textiles, what is called polyester, which is the first fibre for cotton.

Interviewer: Ali Jennings

So, how does this way of recycling PET compare to existing ways that we recycle PET?

Interviewee: Alain Marty

The main way to recycle PET nowadays is called thermomechanical recycling, but it is not really a true solution for the end of life of plastics because during this process, the PET is degraded and there is a loss in mechanical properties, and after several cycles, the material at the end will end up incinerated or landfill. It would be better to develop a closed loop of recycling and the process we have developed is one of the possibilities to create this closed loop of recycling of PET.

Host: Nick Howe

That was Alain Marty from Carbios. You can find the paper he and Ali talked about over at nature.com, or we’ll put a link in the show notes.

Host: Shamini Bundell

Later on, we’ll be finding out how to get molecules really cold. First though, it’s time for the Research Highlights, read to you this week by Dan Fox.

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Dan Fox

You won’t believe how shocking the next Research Highlight is. Did that peak your curiosity? Because it turns out that human curiosity, even about trivial matters, can be so strong that people are willing to risk uncomfortable electric shocks in order to satisfy their inquisitiveness. Researchers in the UK showed volunteers videos of magic tricks. They then offered them the chance to find out how the tricks were performed, but before they could learn the secret, they were given their odds of learning the solution versus their odds of receiving an electrical shock. Volunteers then had to decide on whether it was worth taking the gamble to satisfy their curiosity. Even when the risk of being shocked was 50% or more, some volunteers still took the chance. Scans of their brain showed that anticipation of having their curiosity satisfied activates similar neural pathways to those involved in expecting a reward. If you’re still curious about that research, you can read it in full at Nature Human Behaviour.

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Dan Fox

Oktoberfest, the festival that takes place in Munich, Germany each year, is renowned worldwide as a celebration of beer, bratwurst and polka. But it’s also known by researchers for the excessive natural gas produced at the event site. Now, a team from Munich have measured methane emissions around the festival and found that levels during the carnival were up to 100 parts per billion higher than in the time afterwards. The researchers estimate that the majority of this extra methane leaks from gas appliances used to heat the festival and cook meals for the 300,000 daily visitors. But they also calculate that a stinking 22% of the emissions are produced by the revellers themselves. The authors hope that their work could help form the basis for future policies to reduce the emission footprint of large festivals. Sniff out that paper in full at Atmospheric Chemistry and Physics.

[Jingle]

Host: Shamini Bundell

Next up on the show, things are getting cool… really cool. As temperatures go down, atoms and molecules start moving less and less. But when they get to ultracool temperatures – close to absolute zero – then things start to get really interesting.

Interviewee: Hyungmok Son

We can reach the cold quantum degenerate regime, where individual particles become indistinguishable.

Host: Shamini Bundell

This is Hyungmok Son, a physicist who works on getting things super cold. When atoms or molecules cool down to this degenerate region, they can form a special kind of matter, known as a Bose–Einstein condensate. Here the atoms or molecules can act as if they’re one quantum object, so quantum effects that are otherwise hard to study get amplified, allowing physicists to explore a range of puzzling phenomena. Physicists have managed to cool atoms down close to absolute zero and probe the peculiar quantum states that emerge, but to get molecules – bonded groups of atoms – close to absolute zero has proved much more challenging. This week in Nature, Hyungmok and his colleagues think they’ve cracked the problem by mastering a long-sought technique called collisional cooling. Reporter Lizzie Gibney gave Hyungmok a call and started by asking him why researchers are so keen to cool molecules.

Interviewee: Hyungmok Son

So, these molecules can rotate and vibrate – something that singular atoms cannot do – and using these rotations and vibrations, we can control their quantum behaviour. And also, if the one atom is different from the other, the molecules become polar, and this polarity empowers these molecules to strongly interact with each other, even at long distance, which is something that atoms cannot really achieve either.

Interviewer: Lizzie Gibney

So, the kind of tools that you have to play with your molecules, you have a lot more tools to play with your molecules than you would if they were atoms, so you can do cooler things?

Interviewee: Hyungmok Son

Exactly, so we have more to control their interactions or quantum states, basically.

Interviewer: Lizzie Gibney

So, describe to me what this collisional cooling actually involves.

Interviewee: Hyungmok Son

Collisional cooling is like a refrigerator. Basically, you have a bunch of colder particles that remove heat from the sample that you want to cool. A key in this technique is that the particles should effectively exchange energy through so-called ‘good collisions’ without heating or disturbing each other – so-called ‘bad collisions’. People are pretty good at cooling certain types of atoms, so using those well-cooled atoms as refrigerator for molecules seemed very ideal. However, they are just more than a pair of atoms. The complexity makes them tend to have destructive bad collisions with atoms.

Interviewer: Lizzie Gibney

And in this case, how were you able to encourage the good collisions over the bad ones?

Interviewee: Hyungmok Son

So, we let our molecules and atoms spin in the same way. By doing so, we supressed that bad destructive collisions, so atoms and molecules efficiently exchange energy by colliding without much destruction and heating. So, in our work, we have cooled atoms or molecules from 2 microkelvin to 200 nanokelvin using sodium atoms as refrigerators, and this is the first successful demonstration of collisional cooling of molecules down to nanokelvin temperatures.

Interviewer: Lizzie Gibney

So, we’re talking, what, trillionths of a degree above absolute zero? Is that cold enough in order to see this kind of amplified quantum behaviour that you’re looking for?

Interviewee: Hyungmok Son

If we get molecules to be about five times colder than what we have achieved so far, we will reach the quantum degenerate regime, and we think by solving some technical limitations in our experiment, we’ll be able to cool our molecules further down to that quantum degenerate regime.

Interviewer: Lizzie Gibney

So, you’re on the brink of being able to do that?

Interviewee: Hyungmok Son

Right, so, the final temperatures of our molecules are not limited by fundamental problems but rather technical problems. By upgrading our apparatus, we believe we can basically bring the temperature of the molecules down to even closer to quantum degenerate regime.

Interviewer: Lizzie Gibney

And what are some of the applications then that you hope to be able to do or the kind of quantum states that you hope to be able to create once you have got down to that region?

Interviewee: Hyungmok Son

There are many directions we can pursue once we can make quantum degenerate molecules. For instance, we can use molecules as qubits to make quantum computers out of, and also, we can simulate some very exotic quantum materials using these molecules. And also, we can study chemical reactions between molecules or even molecules and atoms at the quantum level.

Interviewer: Lizzie Gibney

And so, these kinds of vibrations and rotations and things that a molecule is able to do, does that mean that you have a much greater variety in the quantum states and the experiments that you can do than you would if you were doing them just with atoms?

Interviewee: Hyungmok Son

Exactly, so rotations and vibrations, this is something that you cannot really use out of the atoms.

Interviewer: Lizzie Gibney

This is a whole new kind of quantum world that hopefully we’ll be exploring soon.

Interviewee: Hyungmok Son

I hope so too.

Host: Shamini Bundell

That was Hyungmok Son from Harvard University in the US. You can find his paper over at nature.com, or there’ll be a link in the show notes.

Host: Nick Howe

Now, we’re not going to have a News Chat for a while, but don’t forget you can check out Coronapod. The next episode is on Friday and you can find it on all our usual channels.

Host: Shamini Bundell

For now, though, Dan Fox is back with a mysterious Research Highlight.

Dan Fox

An intergalactic murder mystery has been solved, revealing a long-sought-after culprit – an intermediate-mass black hole. Intermediate-mass black holes are black holes smaller than their supermassive siblings that exist at the centre of galaxies but larger than stellar-mass black holes formed by collapsing stars. They have long been theorised to exist but have avoided definite detection until now. Astronomers got their first inkling that something was out there when they detected a burst of X-rays, a tell-tale clue of a black hole tearing a star apart. To investigate, the researchers used two X-ray observatories and the Hubble Telescope and discovered the source of the flare to be a dense cluster of stars, exactly the sort of shady hangout that an intermediate-mass black hole could be found in. Caught in the act of devouring a star, the X-ray glow produced allowed them to estimate the object’s mass and confirm their suspicions that it was the wanted medium-sized black hole. Read the rest of that casefile at Astrophysical Journal Letters.

Host: Nick Howe

That’s it for this week. Don’t forget, if you feel like reaching out to us, you can find us on Twitter – we’re @NaturePodcast.

Host: Shamini Bundell

Or if Twitter isn’t your thing, you can send us an email – it’s podcast@nature.com. I’m Shamini Bundell.

Host: Nick Howe

And I’m Nick Howe. Thanks for listening.