Anne Pringle (U. Wi.) 1: Introduction to Fungi


Hi. My name is Anne Pringle, and I’m a professor of Botany and Bacteriology at the University of Wisconsin, Madison. And today I’m going to talk to you about fungi. So, it’s a challenge to try to teach about fungi in a short talk, because there’s a lot to say. But I’m gonna try to tell you some interesting things and hopefully teach you a lot about what the fungi do in our world. If you think about fungi, one of the things that you may think about is the fact that they cause disease. And it’s true. Fungi do cause disease. The reason that this frog is on the cover of nature with the label “Fear of Fungi” is that there is a fungal disease of amphibians that’s spreading through the world, and amphibians are greatly at risk because of this fungal disease. But fungi don’t only cause disease. And it might not, in fact, be their most important role in our world. Fungi are also mutualists. What you’re looking at in this image is seedlings of pine and you can see the roots of those pine seedlings in the soil, in that black matrix. But most of what you’re looking at when you look at this image is a network of fungi. And that network, those fungi, are scavenging nutrients from places in the soil where plant roots can’t reach. And they’re bringing those nutrients back to the plant in exchange for carbon compounds. It’s a classic exchange of benefits or resources, and the truth is, as you walk around in the world, most plants are not growing alone. Plants are growing with fungi; they’re engaging in these mycorrhizal symbioses. And, by the way, the word mycorrhizal sounds complicated, but it’s not. It simply means fungus/myco, rhizal/root. So, a mycorrhizal anything is a fungus-root anything. So, fungi cause disease, there are mutualists… I find that one important role that fungi play in our world is particularly… particularly hidden. It’s… it’s something that people really don’t think about a lot. And that’s the fact that fungi are decomposers. Fungi eat dead things. They eat dead plants, dead animals. They break them apart and we’re going to talk about that as well. Above all, what I’d really like you to appreciate about fungi, as I talk about them, is that they’re enormously diverse. They’re beautiful, complex organisms. They’re common. They’re part of your everyday world. They take all kinds of forms and colors in nature. You’re looking at a… a very beautiful Amanita muscaria. If you’ve… if you have thought about fungi this might be a species that you’ve encountered. It’s iconic. It’s often, for example, in books of fairytales, you’ll see it. But there are also quite a lot of lichens in this image as well. And what you can’t see, but is surely true, is there are a lot of other kinds of fungi hidden within the substrates that you’re seeing, for example, hidden within the plant within the soil, as well. So, let’s talk about what fungi do in the world. And let’s start by talking about this very real… real… real role that they play for us, and in the world, and for lots of different kinds of organisms. Fungi do cause diseases. They cause the disease that’s decimating amphibians. But they also cause diseases that impact humans more directly. There are lots of examples that I could pick to illustrate this point. This is one of my favorite examples and it’s a historical one. And the map you’re looking at is a map of counties in Massachusetts, and the more green the county is the more Irish-Americans live there. If you’re Irish-American, there is a very good chance that the reason you live in North America is because of a fungus. Actually, it’s the potato blight, which is a fungus-like organism. And it’s true that when I say the word fungus I mean things that are in a kingdom labeled as fungi. But I also mean a lot of organism… other different kinds of organisms that aren’t in that true kingdom, but they’re not plants and they’re not animals. They’re a kind of diversity that’s been tough for us to understand. And so, for the moment, they still fall within the study of people who call themselves mycologists. And potato blight is one of those. When potato blight emerged in Ireland, it was at a moment when the potato was the most important crop, in the sense that this is what people really relied on for their food. The potato blight decimated potato crops. At least one million people died, but that estimate is rather fuzzy. I don’t think we really have good numbers for how many people died because of this disease that killed the crops. Lots of other people, at least one-half million, emigrated. If you want to know more about it, there’s a fantastic book — it’s older — called Advance of the Fungi, that was written by a man named Large, and he pointed out the potato blight fungus had revealed itself as a new and formidable enemy of mankind. And it continues to be a disease that we struggle with today. So, this is one story about how one disease really shaped our world. It shaped how Ireland is… Ireland has still not recovered demographically from the potato blight. There’s still fewer people… people in Ireland now than there were before 1845. And certainly, the United States has been shaped by the immigrants that came from Ireland in the wake of this disease. That’s a specific story. What about more generally and more globally, perhaps? What you’re looking at is an image of a wheat… wheat plants that are infected by a rust fungus. And it’s called a rust fungus because it looks like rust; it has these very orange… orange, rusty-looking pustules on the crop. So, this wheat is not… is no longer edible. And I think the quote illustrates very nicely… “in the United States alone, despite our attempts to control disease, each year crops worth at least $9.1 billion”, I would say, “are lost to diseases”. That’s a… that’s a huge impact on our economy, caused by diseases. And the total pre-harvest and post-harvest food losses to pests in the United States is about 40%, and for the entire world is about 45% of all food crops. We lose a lot of our food that we grow to disease. And that’s clearly… clearly a very… a very important impact that diseases have on humans. How does that translate to other realms of human society? This is a graph that’s pointing out the link between food insecurity, caused in part by disease, and political instability, from the New England Complex Systems Institute. What you’re looking at on… on the vertical axis is the food price index that’s… that’s created and measured by the United Nations. And it’s… it’s essentially the price of food, as measured by… by looking at a particular subset of different kinds of foods and… and measuring their price in real time through the years. And what you can see is that there are times, which actually, intuitively, all know… we all know from shopping at the grocery store, that some kinds of food are more expensive than they are at other times. And you can see, for example, in 2008 it was a moment when food in general, across the globe, was very expensive. And that does have in part to do with diseases that we’re decimating certain kinds of crops, like wheat. It’s also true that, at those moments when food is very expensive, there is a correlation with violent protests. So, red lines mark, for particular countries, and the numbers are the numbers of violent protests… the red lines mark how many violent protests are happening in a particular place at a particular time. And it’s fairly striking and perhaps not surprising that, when food is expensive and there’s food insecurity, there’s also political instability. So, this may not be something you’ve ever thought about before — the link between growing food, diseases that limit our ability to grow food, and politics. These are some of the diseases that we think about, nowadays, when we think about food insecurity: potato blight, still, that I talked about before; wheat stem rust; and then other things, for example, black sigatoka, which is devastating banana crops, currently, across the globe, and is a reason why the Cavendish banana that you’re very familiar with might soon be replaced with some other variety of banana as you go to the grocery store. How do you control fungal diseases? Well, interestingly, it’s true now and it’s been true for a very long time that there are two… there are two mechanisms that growers use to control disease. The first is breeding. You can breed a wheat plant — and you’re looking at different varieties of wheat, there — that are more or less resistant to a particular strain of a particular disease. And so this is one way we try to stay ahead of diseases, is breeding crops that… that simply can’t be infected. The other major means of control is fungicides. What’s interesting about fungicides is that you have to apply them either before or as a disease is reaching your crop. And diseases usually spread with… with propagules called spores. So, you have to… spores are the dispersive agent of fungal diseases, typically. So, you have to spray as those spores are reaching your crop. If your crop is already infected, if the spore has germinated and the fungus is growing inside the wheat, for example, it’s tough to get out and you can’t control it very well. Fungi also cause diseases of humans. Typically, if you take an X-ray of a lung, it should be quite clear. You’re seeing an extra here that’s not clear. If you look in the lung spaces, you can see cloudy parts that you can’t see through very well. Those cloudy bits are where a fungus is growing. This is a fungus, a species of Aspergillus, that we all breathe every day. And so something has happened in this human — perhaps this human is immunocompromised. And because of that particular state of that human, the fungus has been able to take a hold and grow, and that’s what you’re seeing here. It’s very tough to treat fungal diseases of humans. And that’s because, in contrast to what you might have learned when you took high school biology, fungi are not related to plants. I’m a professor of Botany, but that’s historical. Fungi are more closely related to animals, and to humans, than they are to plants. And that means that any antifungal that’s developed is quite likely also to be an antihuman, if that makes sense. Those drugs that kill a fungus may in fact do a lot of damage to a human being as well. This is a phylogeny that illustrates that point nicely. You can see the fungi over here, humans are metazoans. That’s the modern view. And that’s… that’s… not the modern view, it’s what we… it’s… this is the fact… this is what we know now. Plants are very far away from fungi. So, fungi are diseases, but they do a lot else in our world as well. They’re not just diseases. And I think an underappreciated aspect of what they do for us — also for crops, by the way — is serve as mutualists. They provide benefits to plants, to animals — we won’t talk about that so much today — and in return get benefits, a classic mutualistic symbiosis. Here’s the field in North Carolina where I used to do quite a lot of work. When you walk in this field, you see the plants. You see the above-ground structures. You’re not seeing what’s hidden inside the soil. But if I could dive with you underground, to look at what’s going… give you some magic goggles to peer inside the roots, what you would see is a lot of structures that look like this. This is an arbuscule of an arbuscular mycorrhizal fungus. And you’ll find these quite commonly in… all the time, almost in any roots you look at, you’re gonna find these little tree-like structures. This is where the fungus is giving a benefit, in this case it’s often phosphorus, to the plant, in exchange for carbon compounds. So, these associations these arbuscular mycorrhizal fungi, are common with plants like grasses, for example. The picture I showed you of the book, that’s a tree and an ectomycorrhizal fungus. So, that’s a different group of fungi that forms associations with trees. When I started working in this field, a common idea was that the diversity of arbuscular mycorrhizal fungi would be low, was low. In any given field, you might find one or a few species. In this field, it turns out that that’s not true at all. And we found lots of different kinds of species in this field, including many that were new to science. Describing species is really hard work, actually. And so, for many of these species, we knew they existed and we were content to know that they existed, and to talk about them and use them in experiments. But we didn’t actually give them Latin binomials — we didn’t name them formally. But here they are and they’re beautiful. This is a common thing that happens when you go to really any habitat. You could go to your own backyard and, if you were very careful and you wanted to know what was there and did an exhaustive survey, you would find new species of fungi. If you’re passionate about naming a new species for your great-aunt Petunia, you want to be a mycologist. You want to come join me and explore the biodiversity of this amazing kingdom. We think that we have names for something like 5% of the fungi that are on our planet. So, we… we have perhaps 74,000 names, but we think something between 1.5 and 6 million species exist. And the fact that that’s the range I give you suggests a lot about what we really don’t know about fungal biodiversity. And some of these forms are very familiar, the classic mushroom for example. But some of these forms are not so familiar, for example, the fungi that grow on the backs of lady beetles. Or, I would argue, the yeasts. If you’re a brewer or a baker, you know about one particular kind of yeast, but there are a lot of other kinds of yeasts out there — hundreds, thousands of species of other kinds… kinds of yeasts in the world. And they take amazing colors and amazing shapes as well. There are a lot of them. But what happens to biodiversity that we don’t have names for. Well, this is one thing that can happen to the biodiversity of things we don’t have names for. This is actually a picture of my field site, which, shortly after I stopped working there, was turned into an art museum. And it’s almost certainly true that the fungi that we once worked with no longer exist in this field, and I don’t know if they exist anywhere else in nature. When you turn a… a grassland or an old field into a lawn, generally you fertilize that lawn. And if you fertilize the lawn then you kill the fungi. And I think this is something quite profound, that’s worth thinking about as we think about what we want to save or not save on our planet. Conservation biology generally focuses on plants and animals. It more rarely considers these hidden parts of biodiversity that are not so obvious to human eyes. And I think, at this point, a quote about bacteria seems [relevant], and I’m going to read it with you. “I make no apologies for putting microorganisms on a pedestal above all other living things. If the last blue whale choked to death on the last panda, it would be disastrous and sad but not the end of the world. But if we accidentally poisoned the last two species of ammonia oxidizers,” or some other critical microbe, “that would be another matter. And it could be happening now and we wouldn’t even know,” because we don’t even have names for most of what’s out there. So, we don’t know what we’re losing or what we’ve already lost. Why do we care if we’re losing them? Well, with arbuscular mycorrhizal fungi, their role in nature does intrinsically, immediately argue for some careful thought about their preservation. So, I’m gonna walk you through a series of experiments that have been duplicated, think, thousands, probably tens of thousands of times. These are called big plant, little plant experiments. And it’s as simple as growing a plant with an arbuscular mycorrhizal fungus or without an arbuscular mycorrhizal fungus, just to see what happens. And this is an experiment that I actually did as part of my dissertation, quite some years ago now. So, you’re looking at different species of plants in these little different individual pots. And the data, just as many people have discovered and replicated through the years, show you that when a plant is growing without any kind of fungus at all it’s a smaller plant. It doesn’t grow as well as a plant that’s growing with an arbuscular mycorrhizal fungi. So, plants are bigger when they grow with fungi. It’s also true that what species a plant is grown with matters very much. Here, you’re looking at a wild onion plant. And it’s either going with one species of fungus or another species of fungus. And you can see there’s a dramatic difference in the growth of the onion, depending on what species it’s growing with. So, it’s not true that any mycorrhizal… mycorrhizal product that you might buy will offer an equivalent benefit. You have to pay some attention to what kind of species you might be using in your garden, for example, if you’re someone who’s buying these kinds of fungi off the shelf in gardening stores. So, those are arbuscular mycorrhizal fungi. That book image I showed you is an ectomycorrhizal fungus, and this is a big plant, little plant experiment with an ectomycorrhizal fungus, and it’s maybe many people’s favorite ectomycorrhizal fungus. This is the… a truffle. And this is not just any truffle, this is the truffle that you eat, that you cook with, that you stick in your rice to make your rice smell great, that you shave over your… your scrambled eggs to make your scrambled eggs fantastic. And you can see that these oaks, these trees, when they grow with that truffle they’re much bigger — again, it’s the big plant versus the little plant — than when they’re grown without the truffle. And the experiment is quite dramatic, as it often is when you do this kind of experiment. These kinds of associations have evolved repeatedly, over and over again. There’s not a single origin to this kind of mutualism. And so, for example, North American pines growing with Amanita, that’s an interaction that involved entirely… and Amanita is the name of this mushroom, by the way… this association evolved entirely separately, independently, from the association of Nothofagus, which is a southern hemisphere genus of tree, with these truffles. In this case, these are Australian truffles, not the kind of truffle that you eat. And if you want to know more about convergent interactions, you can see one of my other talks on iBiology, where I’m gonna dig into this in a little more detail. So, here’s another thing that fungi do. And I really think that this is… this is a role that fungi play in nature that’s that seems pretty cryptic, it seems like it’s a thing that not very many people know about. Fungi are decomposers. They break apart dead stuff. What does that look like? Well, this is what decomposition looks like. So, strawberries that you might leave out on the counter don’t last as strawberries very long. Fungi, like this one, come along and just turn them to mush. That fungus is eating that strawberry. It’s turning the biomass of the strawberry into its own biomass. It’s also using energy and respiring away. And, now, that fungus is gonna sporulate, that’s what the green is, and those spores are gonna leave that china plate and find some other part of your refrigerator to live in, where there are fresh strawberries. So, decomposition is decay. It’s… it’s the blowing apart of biomass and turning it into something else. This process happens not just in your refrigerator. It happens, for example, in soil. So, carbon is an element that’s moved through the planet in… in… through different channels, if you will. And this is an image of those different kinds of channels. We’ll ignore the ocean for the moment. Let’s look at this channel, right here. So, this is… this arrow marks where… marks the impact of photosynthesis on the carbon cycle. So, trees suck carbon out of the atmosphere, out of the air, to build biomass. And if you’ve grown a plant, you know this to be true, right? It stays in the pot, there’s always the same amount of soil, but it gets bigger because it’s pulling carbon out of the air. So, this is a critical part of the carbon cycle. It’s also true that decomposition, this decay of residues, is a critical part of the carbon cycle. So, this is what’s happening when organisms like fungi blow apart old leaves and old trees and old squirrels. And they… they in the process of… of growing and metabolizing they release a lot of that carbon back to the atmosphere. And it’s also a critically important part of the carbon cycle. So, if you want to think about the Earth and biogeochemical cycles and the… the big picture of how elements move through the world, fungi are a huge part of that. And say, for example, in many forests, without fungi, you’d have an enormous accumulation of just dead stuff on the forest floor. Okay, that’s the forest. If you never walk in a forest, maybe you’re not so interested in forests. What about your town? If you have street trees? And in the fall, you rake up all those leaves and you stick them in those brown bags and you put them on the… on the side of the street. Or your compost. If you have a compost bin or you put out compost, the reason that that doesn’t just stay as it is forever, like plastic in a landfill, is because of the fungi. The fungi come for free — your town doesn’t have to buy them, you don’t have to buy them for your compost bin. The fungi come and they establish and they grow and they tear apart all that dead stuff. It’s an enormous service that fungi provide to us. So, I’ve shown you a lot of pictures of different kinds of fungi along our path of talking about their different roles in the environment. And I hope you’ve got a sense of how diverse they are. A last message I want to give you is that, not only are fungi diverse, they’re enormously dynamic. So, a fungus doesn’t just sit there as a mushroom that you observe. There’s a lot going on inside the body of a fungus. One of the things that’s going on is movement of nuclei. Each of these little green dots is a nucleus. So, as a human, you have one nucleus per cell of your body and your eyeball nucleus will never travel down to your foot. But a fungus doesn’t have barriers like that inside it. And when I say a fungus, I should… I should add the caveat that… that when you’re talking about six million species sometimes it’s hard to find generalities. So, this movement of nuclei is not universally true for every species of fungus you might encounter, but it’s true for an awful lot of them. So, in an awful lot of fungi, there are super highways and back roads, all kinds of channels through which there is movement of nuclei and other substances, cytoplasm. It’s not a… it’s a… it’s a much more… there’s a lot going on inside of fungus that you might not have suspected when you walk by a mushroom, wherever you are walking by mushrooms — in the grocery store, perhaps. Why… why is that? All of that… why is there all that movement? What’s going on there? Well, this is again a fungus-like organism, not a true fungi, but it’s become a bit notorious because this slime mold seems to possess something that we want to call intelligence. So, for example, if you put this slime mold in a maze, it can find the shortest path through that maze. So, somehow it’s a really good engineer. And it does that, I think, because of the movements that are happening inside it. So, here you’re looking at a very tiny network, cut from the larger one. And you can see… it’s a time-lapse video… you can see… you can see that the channels are becoming bigger and smaller, depending on how much fluid is inside them. And you can watch and… it’s not… it’s not a very coherent behavior at the moment. But we’re going to add a drop of food right here. There it is. And then that part of the network swells, it absorbs the food, and then there’s an extremely cohorent… coherent, coordinated behavior, these pulsatile contractions that move across the fungus. And I think it’s this coordinated movement that enables this fungus to generate its amazing behaviors. That you can play with on your own at home, if you want. It’s easy to grow, this one. You can have a pet slime mold. When it comes to dispersal… I’ve mentioned spores several times. And there’s… there… I think a commonly held idea is that spores are passively dispersed, just depending on the wind and the weather around a particular fungus as it’s releasing its spores. But that not… may not be an entirely… that may not be entirely the right way to think about that either. This is a structure of a fungus, a sporocarp, that’s releasing spores. And what I’m going to show you is that it doesn’t just release its spores one at a time. It releases this jet of hundreds of thousands of spores, and by doing that this fungus creates its own wind. It’s not a passive process at all. This is called puffing. And you can see all those spores moving the air and, as they move the air, they’re creating a wind, and then they’re traveling in that wind that they created to get to places that they want to go. So, the takeaway is that fungi, which are diverse and by and large unknown, are complex, dynamic organisms that play critical roles in your life, as diseases, yes, but also as mutualists, and in the environment as well. And, if you haven’t already discovered this for yourself, they are an awful lot of fun to find, as my daughter would tell you. And I really want to thank the Pringle laboratory, everyone who’s been with me all along the way, for taking this amazing journey through the kingdom with me. And if you’d like to know more, these are resources that you could go to on the web to learn a lot more about fungi. Mushroom Observer is a place where you can record your… what you’ve picked, where you picked it, and compare it to other things that people have… have looked at, and get some help with identification. This has just a whole set of fantastic videos and information about fungi, generally. Mushroom Expert, as well, if you’re interested in identifying things in… in North America, in particular. This uhh… genera of fungi. This is a great resource. And if you have any questions about human diseases or sick buildings, this is the place to go. Thanks very much for listening.

7 thoughts on “Anne Pringle (U. Wi.) 1: Introduction to Fungi

  1. So when AGW catastrophists assert that plants are phosphor and nitrogen limited (and, therefore, can't benefit from the increased CO2 level), they lie? From this presentation I infer that the increased CO2 level would increase carbohydrate production which would stimulate exchange with fungi.

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