How some fungi learned to eat plastic

HostWe spend a lot of time worrying about plastic piling up in the ocean or sitting in landfills because it feels like something that will just last forever. But it turns out, nature might be starting to see all that trash as a bit of a buffet. How did some fungi actually learn to eat our plastic waste?

GuestIt's a bit of a shock when you first hear about it, but it makes a lot of sense when you look at how fungi have lived for millions of years. They're the world's best cleaners. Their whole job is to find tough stuff that nothing else can eat, like wood or fallen leaves, and break it down into food. About ten years ago, some students from Yale found a fungus in the Amazon that could live on a diet of nothing but plastic. And they found it could do this even without any air, like you would find at the very bottom of a trash heap. Then, a few years later, other researchers found another type growing right in a huge dump in Pakistan. It was happily munching away on a piece of plastic in the dirt. These fungi aren't doing us a favor out of the goodness of their hearts. They just found a new source of energy that nobody else was using.

HostBut plastic is a man made thing. We only started making it in big amounts maybe seventy or eighty years ago. That seems way too fast for a living thing to just learn a new trick like that.

GuestYou would think so, but fungi had a massive head start. Think about a tree. Wood is incredibly tough because of a stuff called lignin. It's the material that makes trees strong and rigid. For a long, long time in Earth's history, nothing could break down wood. When trees died, they just piled up and stayed there. Eventually, fungi figured out how to make these special juices, which we call enzymes, that act like tiny chemical scissors. These scissors are designed to snip through the long, messy chains of molecules that make up wood. It just so happens that the way we build plastic is very similar to the way nature builds wood. We use long chains of atoms called polymers. To a fungus that has spent eons learning how to crack open a tree trunk, a plastic bottle looks like a slightly weird, very smooth branch.

HostSo they're not really learning something brand new. They're just using their old wood cutting tools on a new kind of job?

GuestYeah, that's a great way to put it. They're using their old tool kit. When a fungus lands on a piece of plastic, it sends out these little feelers. It spits out those chemical juices to see if they can catch onto anything. If the juices manage to break a few links in that plastic chain, the fungus realizes, hey, there's sugar in here. There's energy. Once it gets a taste, it starts making more of those specific juices to finish the job. It breaks the plastic down into smaller and smaller bits until it can pull them inside its own body to use as fuel. In the case of that fungus from the Amazon, it was eating a type of plastic called polyurethane, which is used in things like garden hoses and foam. The chemical bonds in that plastic look almost exactly like the bonds the fungus is used to seeing in the wild.

HostI guess my worry is that if they can eat a garden hose, what stops them from eating our houses or the wires in our walls? Is everything we build now at risk of being eaten?

GuestWell, we don't have to worry about our houses melting just yet. These fungi are mostly found in very specific, damp places like rainforests or deep inside landfills. They need a lot of moisture and the right heat to do their work. Also, they're still pretty slow. In a lab, it might take a few weeks or months for a fungus to eat a small piece of plastic film. In the wild, it takes much longer. But the real friction here is that we have made so many different kinds of plastic. Some plastics are like soft wood that the fungi can handle, but others are like solid rock. The stuff we use for soda bottles or milk jugs is much harder for them to get a grip on. Their chemical scissors just blunt against it. So while they're getting better at it, they're not quite ready to take on the whole world of trash.

HostSo we can't just toss some mushrooms onto a landfill and expect it to be gone by next week. Is there a way to make them work faster, or are we stuck with their natural pace?

GuestThat's where the science is headed now. People are trying to find the best versions of these juices and see if we can mass produce them. We might not even need the whole fungus. If we can just take the juices they make and put them into a big tank of ground up plastic, we could turn trash back into raw materials in a few days. It's a way of taking a natural process and turning the volume way up. But even then, we run into a big wall. When a fungus breaks down plastic, it's not just disappearing. It's being turned into other things. Sometimes that's just more fungus, but sometimes it can leave behind chemicals that might be bad for the soil. We have to make sure that in our rush to clean up the plastic, we're not accidentally making a new kind of mess.

GuestThe real puzzle now isn't if they can do it, but if they can do it fast enough to keep up with how much trash we throw away every single day.

HostThe same tools these fungi used to clean up fallen trees millions of years ago might be the very things that help them clear out our soda bottles today.