Fungi: Death Becomes Them - CrashCourse Biology #39

Summary

This script delves into the fascinating world of fungi, highlighting their vital role in decomposition and nutrient recycling in ecosystems. It explores their diverse nature, from beneficial yeasts in bread and beer production to deadly pathogens. Fungi's unique reproductive methods and their mutualistic relationships with plants through mycorrhizae are also discussed, showcasing their complexity and importance in the global food web.

Takeaways

• 🍄 Fungi are a diverse group with both acceptable pronunciations: 'fungi' (fuhn-gahy) or (fuhn-jahy).
• 🌱 Fungi are more closely related to animals than plants and diverged from protists around a billion years ago.
• 🔍 Scientists estimate there are about 1.5 million species of fungi on Earth, with only about 100,000 known to taxonomy.
• 🍺 The single-celled fungus Saccharomyces, or yeast, is crucial for the production of beer, wine, and bread.
• 🤢 Fungi can cause a range of diseases, from athlete's foot to the potentially deadly histoplasmosis.
• 🍞 The fungus Claviceps purpurea can cause serious health issues, including hallucinations and temporary insanity, and is the source of LSD.
• 🦇 Fungi have devastating effects on wildlife, with white nose syndrome killing millions of bats and contributing to amphibian extinctions.
• ♻️ Fungi play a vital role in the global food web by decomposing organic matter and recycling nutrients back into the soil.
• 🧬 Louis Pasteur's research on yeast revealed the process of fermentation, leading to the development of pasteurization.
• 🌳 Fungi are heterotrophs that absorb nutrients from their surroundings, breaking down complex molecules with enzymes.
• 🌿 Mycelia, the network of fungal filaments, can be incredibly dense, with enough hyphae in a small amount of soil to stretch for kilometers.
• 🔍 Fungi can be classified by their interactions with other organisms: as decomposers, mutualists, predators, or parasites.
• 🌳 Decomposer fungi are essential for breaking down lignin in wood and returning nutrients to the soil.
• 🌱 Mutualistic fungi, like mycorrhizae, form beneficial relationships with plant roots, aiding in nutrient absorption.
• 🕷️ Predatory and parasitic fungi can capture prey or feed on living organisms, with some even manipulating host behavior.
• 🧬 Fungi reproduce both sexually and asexually, often producing vast numbers of spores for dispersal.
• 🍺 The process of fermentation by yeast is harnessed in brewing to produce alcohol from sugars.

Q & A

What are the two acceptable pronunciations of the word 'fungi' mentioned in the script?

The two acceptable pronunciations of 'fungi' mentioned in the script are 'fuhn-gahy' and 'fuhn-jahy'.

How many species of fungi are estimated to exist on Earth according to the script?

The script states that scientists estimate there to be about 1.5 million species of fungi on Earth.

What is the role of the fungus Saccharomyces in human activities?

Saccharomyces, also known as yeast, plays a crucial role in the production of beer, wine, and bread, as mentioned in the script.

What is histoplasmosis and how is it related to fungi?

Histoplasmosis, also known as spelunker's lung, is a potentially deadly disease caused by a fungus found in bird and bat droppings, as described in the script.

How does the fungus Claviceps purpurea affect humans when it grows on grains?

When Claviceps purpurea grows on grains, it can cause a range of symptoms including gangrene, nervous spasms, burning sensations, hallucinations, and temporary insanity, as well as being the source of lysergic acid, a compound used to make LSD.

What is the ecological function of fungi in the global food web?

Fungi perform a vital function in the global food web by feasting on the deceased remains of almost all organisms on the planet and converting organic matter back into soil, which supports new life, as explained in the script.

Outlines

00:00

🍄 Introduction to Fungi and Their Role in Life and Death

This paragraph introduces the world of fungi, highlighting their pronunciation and their dual nature as organisms that are plant-like and animal-like. It emphasizes the vast diversity of fungi species on Earth, with a focus on their role in decomposition and their impact on life. Fungi are portrayed as both beneficial, through their contribution to food and drink fermentation, and as harmful, causing diseases and even influencing human behavior through substances like LSD. The paragraph concludes by underscoring fungi's essential role in the global food web, where they recycle organic matter into soil, enabling new life to emerge.

05:01

🌱 Fungi's Decomposition and Mutualistic Relationships

The second paragraph delves into the decomposition process performed by fungi, explaining how they break down complex organic matter into simpler compounds for nutrients. It details the structure of fungi, including their cell walls made of chitin and the mycelium, a network of hyphae that maximizes surface area for absorption. The paragraph also discusses the classification of fungi based on their interactions with other organisms, focusing on decomposers, mutualists, and predators. Decomposers are crucial for breaking down lignin in wood, while mutualists form beneficial relationships with plants, aiding in nutrient absorption through mycorrhizae. Predatory and parasitic fungi are also mentioned, with examples like the soil fungus Arthrobotrys and the zombie ant fungus, Ophiocordyceps.

10:01

🔬 Fungi's Reproduction and Impact on Human Activities

The final paragraph explores the diverse methods of fungal reproduction, both sexual and asexual, and how these processes are distinct from those of other organisms. It explains the lack of traditional male and female roles in fungi and the various mating types that can lead to spore production. The paragraph also touches on the role of pheromones in attracting compatible fungal partners and the lengthy time it can take for sexual reproduction to occur. Asexual reproduction in fungi, such as in molds and yeasts, is also described. The paragraph concludes by acknowledging the significant impact fungi have on human activities, including agriculture and beer production, and thanks the audience for watching the episode.

Keywords

💡Fungi

Fungi are a diverse group of organisms distinct from both plants and animals, playing a crucial role in the ecosystem as decomposers. In the video, they are described as organisms that thrive on death, converting organic matter into soil, which is essential for the cycle of life. The script also mentions the vast number of fungal species on Earth, underlining their diversity and importance.

💡Saccharomyces

Saccharomyces, commonly known as yeast, is a type of fungus with significant industrial and culinary importance. The script highlights its role in the production of beer, wine, and bread, illustrating how fungi can be beneficial to humans. Yeast is also used to demonstrate the process of fermentation, a key concept in biology.

💡Histoplasmosis

Histoplasmosis, also referred to as spelunker's lung in the script, is a disease caused by a fungus found in bird and bat droppings. This term is used to illustrate the darker side of fungi, showing that while some fungi are beneficial, others can cause serious health issues.

💡Claviceps purpurea

Claviceps purpurea is a fungus that grows on grains and can cause severe health effects when consumed, as mentioned in the script. It is notable for containing lysergic acid, a precursor to LSD. This keyword exemplifies the dual nature of fungi, which can be both harmful and a source of compounds with significant effects on humans.

💡White nose syndrome

White nose syndrome is a fungal disease that has led to the death of millions of bats in North America since 2007, as stated in the script. This term is used to highlight the destructive power of fungi and their impact on wildlife populations, emphasizing the ecological role and potential threat of fungal pathogens.

💡Decomposition

Decomposition is the process by which organic matter is broken down into simpler components, primarily by fungi and bacteria. In the video, decomposition is central to the theme, illustrating how fungi recycle nutrients back into the soil, which supports new life and the continuation of the food web.

💡Heterotrophs

Heterotrophs are organisms that cannot produce their own food and must obtain their nutrients from other organisms. The script explains that all fungi are heterotrophs, absorbing nutrients from their surroundings rather than consuming other organisms directly. This concept is key to understanding the nutritional strategies of fungi.

💡Hyphae

Hyphae are the thread-like structures that make up the body of most fungi, growing through and decomposing organic material. The script describes how hyphae form mycelia, maximizing surface area for nutrient absorption, and how they enable fungi to grow and spread, contributing to their role as decomposers.

💡Mycorrhizae

Mycorrhizae are mutualistic relationships between certain fungi and the roots of plants. The script explains how these fungi help plants absorb nutrients more efficiently, while the fungi receive sugars from the plant in return. This keyword is important for understanding the symbiotic relationships in nature and their role in ecosystems.

💡Predatory fungi

Predatory fungi are a type of fungus that actively captures and consumes other organisms, such as nematodes. The script uses the example of the soil fungus Arthrobotrys to illustrate this concept, showing the diverse strategies fungi employ to obtain nutrients.

💡Zombie ant fungus

The zombie ant fungus, or Ophiocordyceps, is a parasitic fungus that infects ants, controlling their behavior to ensure the spread of its spores. This term from the script is used to highlight the fascinating and sometimes macabre ways fungi interact with other organisms, underlining the complexity of fungal parasitism.

💡Spores

Spores are the reproductive units of fungi, which they produce in large numbers to disperse and colonize new environments. The script discusses various methods of spore dispersal, such as by wind, water, or hitching a ride on animals, emphasizing the importance of spores in the life cycle and spread of fungi.

Highlights

Fungi are a diverse group with both acceptable pronunciations: 'fungi (fuhn-gahy)' and 'fungi (fuhn-jahy)'.

Fungi diverged from protists about a billion years ago and are estimated to have around 1.5 million species on Earth.

Scientists have formally identified approximately 100,000 species of fungi.

Fungi are involved in both beneficial and deadly processes, including the production of beer and wine, as well as diseases like athlete's foot and histoplasmosis.

The fungus Claviceps purpurea can cause hallucinations and is the source of lysergic acid, a precursor to LSD.

Fungi contribute to the extinction of species such as bats affected by white nose syndrome and amphibians threatened by chytrid fungi.

Fungi play a vital role in the global food web by decomposing organic matter and recycling nutrients back into the soil.

Louis Pasteur's research on yeast led to the understanding of fermentation and the development of pasteurization.

Yeasts obtain energy through anaerobic respiration, breaking down sugars into alcohol, carbon dioxide, and flavors associated with beer.

Fungi are heterotrophs that absorb nutrients by secreting enzymes to break down complex molecules.

Multicellular fungi grow through hyphae, which form a mycelium to maximize nutrient absorption.

The largest known organism by area, a honey mushroom in Oregon, is a vast network of interconnected hyphae.

Fungi can be classified by their interactions with other organisms: decomposers, mutualists, predators, and parasites.

Decomposer fungi are essential for breaking down lignin in wood and returning nutrients to the soil.

Mycorrhizae are mutualistic relationships between fungi and plant roots, facilitating nutrient exchange.

Predatory fungi like Arthrobotrys capture prey such as nematodes, while parasitic fungi can control their hosts, as seen with the zombie ant fungus.

Fungi reproduce both sexually and asexually, often producing vast numbers of spores for dispersal.

Sexual reproduction in fungi involves a unique process without the concept of male and female, relying on chemical signals and compatible mating types.

Asexual reproduction in fungi, such as in yeast, can occur through cell division or bud formation.

Fungi are crucial to various industries, including agriculture and brewing, due to their role in decomposition and fermentation.

Transcripts

Hello and welcome to the wonderful world of fungi (fuhn-gahy),

or fungi (fuhn-jahy). Both are acceptable pronunciations.

But I say fungi because it's fungus. Not fun-jus.

Though fun-jus is also fun to say.

Fungi are a little bit like plants,

and more like animals than you might think.

They diverged from protists about a billion years ago,

and today scientists estimate that there are about 1.5 million

species of Fungi on the earth, though in a formal, taxonomic way,

we only know about 100,000 or so of them.

And those that we have met are wonderful, weird, and,

in some cases, deadly.

And the fact is, death is pretty much what fungi are all about.

Sure, there are the fun fungi, like the single-celled Saccharomyces,

also known as yeast.

Without them, we wouldn't have beer, wine or bread.

It's also true that fungi are responsible for all kinds of diseases,

from athlete's foot to potentially deadly histoplasmosis,

aka spelunker's lung, caused by fungus found

in bird and bat droppings.

Fungi can even make people crazy.

When the fungus Claviceps purpurea grows on grains used

to make bread and beer, it causes gangrene, nervous spasms,

burning sensations, hallucinations, and temporary insanity.

One compound in this fungus, lysergic acid,

is the raw material used to make LSD.

And finally there's the destruction that some fungi bring onto

other animals: More than 6 million bats in North America have died

since just 2007, due to a fungal disease called white nose syndrome.

And a fungus has been implicated in several extinctions

of amphibians and threatens many more,

perhaps as many as a third of all amphibians on Earth.

But none of this is what I mean when I talk about fungi and death.

While some members of the fungus family are total bummers,

all of them together perform perhaps the most vital function

in the global food web: They feast on the deceased remains

of almost all organisms on the planet.

And by doing that, they convert the organic matter that we're

all made of back into soil, from which new life will spring.

So, fungi: They thrive on death, and in the process,

make all life possible.

Aha! You Didn't expect to see me in the chair so soon!

But before we go any deeper into the kingdom fungi, I wanted

to make a toast to Louis Pasteur in the form of a Biolo-graphy.

By Pasteur's time, beer had been brewed for thousands of years

in cultures all over the world.

Some experts think it may have been the very reason that our

hunter-gather ancestors started farming and cobbled together

civilization in the first place.

But for all those millennia, no one understood how its most

important ingredient worked.

Until brewers could actually see what yeast were doing,

the magic of fermentation was... essentially magic.

Pasteur himself was never a big beer drinker, but part of his

academic duties in France required him to help find solutions to

problems for the local alcohol industry.

And as part of this work, in 1857, he began studying yeast under

a microscope and discovered that they were in fact living organisms.

In a series of experiments on the newfound creatures,

he found that in the absence of free oxygen, yeast were able to

obtain energy by decomposing substances that contained oxygen.

We now know that Pasteur was observing yeast undergoing the process

of anaerobic respiration, aka fermentation, breaking down the sugars

in grains like malted barley, and converting them into alcohol,

carbon dioxide and the range of flavors that we associate with beer.

Along the way, Pasteur also discovered that beer was often

contaminated by other bacteria and fungi.

The growth of these beer-spoiling microbes, he found, could be

thwarted for up to 90 days by keeping beer between

55 and 60 degrees Celsius for a short period of time.

Today, we call that heating process pasteurization, and it's used

in everything from milk, to canned foods, to syrups, to wines.

For our purposes, the thing to hold onto here is,

Pasteur discovered that yeasts decompose sugars to get energy.

And it turns out, most fungi spend most of their time decomposing

all kinds of organic matter.

Often the matter is dead when fungi get to it, but not always.

When a tree, or a person, or a deer keels over,

fungi move in and start the work of decomposition.

Same goes for that orange you forgot at the bottom of the fruit bowl.

If it weren't for this fungal function, plants, and the animals

that eat them, couldn't exist because the elements that

they take from the soil would never return.

Thankfully, the decomposition performed by fungi recycles

the nutrients for the enjoyment of plants and animals

as well as for other fungi.

All of this points to one of the main traits

that all fungi have in common.

From single-celled yeast to giant multicellular mushrooms, fungi,

like us, are heterotrophs.

But instead of eating, they absorb nutrition from their surroundings.

They do this mostly by secreting powerful enzymes that break down

complex molecules into smaller organic compounds,

which they use to feed, grow, and reproduce.

Most multi-cellular fungi contain networks of tiny,

tubular filaments called hyphae that grow through

and within whatever they're feasting on.

Unlike plant cell walls, which are made of cellulose,

the cell walls of fungi are strengthened by the nitrogenous

carbohydrate chitin, the same material found in the exoskeletons

of insects, spiders, and other arthropods.

The interwoven mass of hyphae that grows into the food source

is called the mycelium, and it's structured to maximize

its surface area, which as we've learned in both plants and animals

is the name of the game when it comes to absorbing stuff.

Mycelia are so densely packed that 1 cubic centimeter of rich soil

can contain enough hyphae to stretch out 1 kilometer

if you laid them end to end.

So as hyphae secrete the digestive enzymes, fungi use the food

to synthesize more proteins, and the hyphae continue to grow,

allowing the fungi to conquer new territory and grow even more.

As a result, fungi can get crazy big. Record-holding big.

A single honey mushroom in the Blue Mountains of Oregon

is thought to occupy some 2,386 acres.

By area, the largest organism on the planet.

Now there are all kinds of crazy ways that fungi are classified,

but probably the easiest and most useful is organizing them by how

they interact with other organisms.

The straight-up decomposers that break down dead stuff,

the mutualists, which form beneficial relationships

with other organisms, especially plants,

and then there are the predators, and the parasites.

Decomposer fungi secrete enzymes that break down and absorb

nutrients from nonliving organic material, such as that tree

that nobody heard fall in the forest.

In fact, the ability of fungi to break down lignin,

which is what makes wood woody, and break it into glucose

and other simple sugars is crucial for the cycle of life.

They're pretty much the only organism that can do that.

They can even decompose proteins into component amino acids.

Basically, all the black bits in the soil in your backyard

are tiny fragments of former plants digested by fungi.

Mutualist fungi are a smaller group.

Many have specialized hyphae called haustoria that tangle

themselves with plant roots for the benefit of both organisms.

These guys help plants absorb nutrients, especially phosphates,

by breaking them down more efficiently

than the roots can themselves.

In turn, the fungi send out their hyphae into the plant's root

tissue and withdraws a finder's fee, basically,

in the form of energy-rich sugars.

These mutualistic relationships are known as mycorrhizae,

from the Greek words "mykes," or fungus and "rhizon" or root.

Mycorrhizae are enormously important in natural ecosystems,

as well as in agriculture.

Almost all vascular plants, in fact, have fungi attached

to their roots and rely on them for essential nutrients.

Growers of barley, the main ingredient in beer,

will even inoculate barley seed beds with specific

mycorrhizal fungi to help promote growth.

Other fungi aren't nearly so kind to their hosts.

Predatory fungi actively capture prey with their hyphae,

the soil fungus Arthrobotrys uses modified hoops on its filaments

to snare nematodes and absorb their inner tissue.

Then there are the parasites, those fungi that feed on living

organisms without killing them, at least for a while.

Take one of my personal favorites:

the zombie ant fungus, or Ophiocordyceps.

It shoots spores into an ant, where their hyphae grow into its body

and absorb nutrients from non-essential ant organs.

When the fungus is ready to reproduce, it invades the ant's brain

and directs it to march to a cool, moist location in the forest

where its so-called fruiting spores erupt

through the ant's head to spread even more spores.

And just to prove that even fungi have superheroes,

in 2012 scientists discovered that these zombie spores

have themselves been targeted by another parasitic fungus.

Not a lot is known about this ant-saving fungus,

other than it sterilizes many of the zombie spores

through a process likened to chemical castration.

That is so messed up. Weird!

Alright now, since I brought that up,

we should talk briefly about fungus sex.

Fungi reproduce any way they can, either sexually or asexually.

Some species even do it both ways.

But whichever way they choose, most propagate themselves

by producing enormous numbers of spores, much like we saw

in nonvascular plants and the simplest

of vascular plants, the ferns.

But, and this is a big but, sexual reproduction in fungi

isn't like sex in any other organism we've studied so far.

The concepts of male and female don't apply here. At all.

Some fungi reproduce on their own.

Others can reproduce with any other individual

that happens to be around.

And still others can only mate with a member of a different

so-called mating type: they're not different sexes,

they just have different molecular mechanisms that

either make them compatible or not.

Sometimes these types are called plus or minus,

and other times 1 and 2.

In any case, it's still considered sexual reproduction,

because each parent contributes genetic information

when they make with the spore-making.

It all starts with this beautiful chemical mating dance,

as the mycelium from one fungus sends out pheromones that are picked

up and bound to receptors by another willing and able partner.

This binding compels each mycelium to send its hyphae toward the other.

When they meet, they fuse the cytoplasm of their cells,

a stage of reproduction called plasmogamy.

Sometime between hours and centuries later,

yes, it can literally take hundreds of years for fungi to have sex,

this union leads to the production of spores

that each fungus is then able to disperse.

Certain types of fungi, including the tasty morel,

produce spores in sac-like asci contained in

fruiting bodies known as ascocarps.

That is the part you pick when you're wandering through the forest.

Some fungi shoot their spores off into the breeze,

other spores float away on the water.

More enterprising spores will hitch a ride on passing critters,

hopefully to be dropped off somewhere where there's plenty of

nutrients to absorb, so they too can grow, send out sexual pheromones

when their time comes and let their hyphae do the tango.

Finally, for some fungi, sexual reproduction just isn't all

it's cracked up to be.

They'd rather just get it on with themselves.

Some of these grow filamentous structures

that produce spores by mitosis.

These structures are visible, and they're called molds,

the stuff on the orange in the bottom of the fruit bowl

or the heel of the piece of bread that you left for a roommate

who decided to leave it for the other roommate

who thought that you'd rather have it.

In the unicellular yeast, the asexual reproduction occurs by

old-fashioned cell division or the formation of buds

that get pinched off into separate organisms.

Since some species of yeast, like our beer-making friend,

Saccharomyces cerevisiae, convert sugars into alcohol,

brewers create conditions that encourage high rates of yeast

production, like giving them lots of sugar and oxygen,

since more yeast means more alcohol.

So, yeah, fungi! They feast on death,

and they can make us go insane and turn ants

into unholy zombies of the night.

But because of their hard work and strange ways,

they make possible stuff like agriculture and beer

and everything else worth living for.

So thanks to the fungus. And also thanks to you

for watching this episode of Crash Course Biology.

And of course, thanks to the people who helped me put it together.

They're awesome. Thank you guys!

There's a table of contents over there if you want to click on it

and go review any of the stuff that you want to reinforce in your brain.

And if you have questions or comments or ideas for us,

we're on Facebook and Twitter and of course,

we're down in the comments below.

We'll see you next time.