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There’s no denying that fungus is all around us all the time. And not all of it is helpful, but neither is all of it harmful. Here are some of the many functions of fungi.

Hosted by: Stefan Chin

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Original Episodes:
https://www.youtube.com/watch?v=f8SS6DvU_0U
https://www.youtube.com/watch?v=Ai_uHrQNLtQ
https://www.youtube.com/watch?v=9H0dy8fv33M
https://www.youtube.com/watch?v=TL0iYKGBIt4

 (00:00) to (02:00)


(SciShow Intro)

[Stefan]:
From the forest floor to bread to your guts, we seem to be surrounded by our fungusy friends. But those fungus dwellings are so "been there, done that". What about fungus living inside coffee plants. What about the mushrooms that we eat.

Okay, so, regular old mushrooms in omelets and pizza aren't that out of the ordinary, but, there are other reasons people might consume mushrooms. And some studies suggest that they can be medicinal.

So, here's Hank from the past, for the details on that:

[Hank]:
Is it possible that because of the war on drugs we have demonized a treatment for otherwise untreatable diseases? A way to increase personal well-being, permanently treat depression, break the cycle of addiction, ease the transition from life into death. The solution to all of these problems, for many people at least, might be a nice hallucinogenic trip.

Many of the most common mental illnesses come down to a malfunction in the fundamental thing that makes us who we are: our consciousness. Anxiety, depression, addiction, and lots of other afflictions are basically distortions of our sense of self awareness.

Like whether we're actually in danger, in the case of anxiety, or whether we really need those substances that we're craving, as with addiction. I'll leave it to philosophers to decide where consciousness comes from, but medical science has gone a long way in determining how the brain reflects consciousness and how it can be treated when it's sick.

And some neurologists are finding that one of the most effective treatments for diseases of consciousness is unfortunately illegal. Scientists know it as psilocybin, the active ingredient in hallucinogenic mushrooms, and it's pretty similar to other compounds and other psychedelic drugs like LSD and mescaline.

Recent research suggests that it works just like they said in the 1960s: by expanding consciousness. Much of what we associate with consciousness, like emotions, the need to take care of ourselves, and basic self awareness, has been traced to the part of the brain called the cingulate cortex, tucked away near the brain's innermost core.

Specifically, studies have found that this part of the brain, especially its anterior, or front region, is overactive in people with disorders like chronic depression and anxiety.

 (02:00) to (04:00)


In these cases, the cingulate cortex basically goes into overdrive, creating a state of hyper-consciousness with huge uncontrollable spikes in otherwise ordinary emotions and desires that make us the self-aware beings that we are. So, finding a way to loosen up the cingulate cortex could be the key to curing all sorts of mental ailments.

In 2012, a study at Imperial College, London found that a small dose of psilocybin decreased the blood flow to this area of the brain and caused it to communicate less intensely with other parts of the brain. In so many words, it managed to quiet the seat of consciousness.

But psilocybin has also been found to help people facing perhaps the most difficult mental challenge any of us will face: the transition from life to death.

In 2008, researchers at UCLA conducted an experiment on 12 terminal cancer patients who were suffering from severe anxiety and depression. Each subject was given either a placebo or a small controlled dose of psilocybin. After the treatment, all of those who had taken the hallucinogen registered much lower levels of anxiety, describing an increased sense of peace and acceptance with their situation, and all but one of the subjects showed decreased signs of depression.

And it's not just that psilocybin altered the chemistry of anxious, depressed brains. In many cases, it appeared to change the patients themselves. The subjects in these studies not surprisingly experienced hallucinogenic episodes lasting anywhere from 20 minutes to several hours.

And during these trips, many described being able to feel and think about the difficulties they faced more clearly than they could before, thinking about what they'd miss after they died, how their loved ones would cope with their death, and so on.

It was all incredibly intense, of course, but without the cingulate cortex working overtime, those thoughts were no longer filled with the dread and panic that had accompanied them before. And those big thoughts often remained manageable long the trips had ended.

So, these treatments seem to allow patients to actually experience and think about things differently, rather than just medicating their symptoms. And this might help explain why the positive effects of all these studies have been found to last for weeks, even months, in ways that a simple mind numbing drug could never do.

 (04:00) to (06:00)


So clearly, psilocybin sounds promising, but there are also downsides to consider. While psilocybin is milder than the ingredient found in, say LSD, all hallucinogens can cause panic and disorientation and the doses in these experiments were only given in highly controlled environments with mental health workers on hand to help if anything went wrong.

But what makes serious research on psilocybin even harder is that it's illegal just about everywhere, including the mushrooms from which it's extracted and even their spores. In some cases, like the studies I mentioned, scientists were able to get special, very limited licenses that have tons of restrictions on them.

But in most cases research has been brought to a standstill by regulations. Now of course, keeping mind-altering substances off the street is one thing, you'll get no argument from me on that, but it's another thing to hamper research into what could be a breakthrough for mental health everywhere. Maybe the regulators just need to expand their minds a bit.

[Stefan]:
So, fungi have a lot of potential to do good for our minds. But before you go out and buy your "I heart fungi" merch, watch this truly saddening glimpse into a future full of fungi, and maybe devoid of your favourite coffee.

[Hank]:
A lot of us rely on a morning cup of coffee, or several morning cups of coffee, to get us going. But the taste and the quality of that coffee might not stay the same forever. Climate change has the potential to not only shift where and how we grow coffee in the future, but affect whether it can be grown at all.

Whether you’re a coffee aficionado who obsesses over acidity, aroma, and brew method, or you hastily chug some corner-store instant blend on the go, climate change means bad news for your beans. There are lots of different blends and styles of coffee, but we usually just drink two types.

The most famous is Coffea arabica. The other is its less celebrated cousin Coffea canephora, also known as Robusta. Most of us sip Arabica for our daily cup of Joe. But if you get your fix from instant coffee, it’s probably Robusta, which is not considered quite as tasty.

The Arabica coffee plant is pretty particular. It grows best in wet and cool mountain regions. Unfortunately for Arabica, and for us, climate change is bringing a slew of problems to those higher-altitude coffee-growing areas. That’s especially true in places where Arabica coffee grows wild,

 (06:00) to (08:00)


In the humid, shady mountain forests of Ethiopia and South Sudan. The genetic diversity found in these wild plants might hold the key to making coffee more resilient to climate and disease in the future.

But climate change is increasing temperatures and shortening wet seasons in these areas. That makes the outlook not so good for wild coffee forests. By 2088, we could see a 50-80% drop in Arabica populations, which could be enough to land them on the endangered list. Combine that with deforestation, and this special species of bean could be at greater risk of extinction.

While Robusta is definitely more, well, robust when it comes to environmental changes, climate change is shrinking its available growing range too. And as temperatures rise, both species are being hit harder by pests, like the coffee berry borer. This species of bark beetle is a serious enemy of coffee plants.

It used to attack only plants growing below certain elevations. That minimized its impact, since coffee is grown at high altitudes. But with hotter weather, this beetle is expanding its range into higher ground, and appearing in coffee plantations. Warmer weather is also encouraging a number of fungus species to move into Arabica and Robusta territory.

One of the most notorious is coffee rust, which turns the leaves a rusty orange. When coffee rust arrived in Sri Lanka in the 19th century, it wiped out the entire industry in ten years. Coffee rust also followed the coffee industry to Central and South America, where higher heat and humidity due to climate change made plantations vulnerable to infections.

In a short time, the fungus caused billions of dollars in damage and lost profits. And because climate change is shrinking coffee-growing habitat, there are fewer places left for coffee growers to flee this fungus, and other diseases.

Even if we can keep farming Arabica in the future, lower quality growing environments might negatively impact flavor, literally leaving a bitter taste in your mouth. The amount of shade and differences in microclimates change the look, smell and taste of coffee beans.

The best specialty coffee comes from natural, shady coffee-producing forests, since Arabica grown under high sun exposure takes a hit in terms of bean quality.

 (08:00) to (10:00)


Also, in healthy coffee-producing forests, higher diversity in insect and orchid species appears to play a role in coffee quality. In fact, coffee connoisseurs can differentiate between coffees grown in different elevations and conditions, sort of like how some sommeliers can taste variations in wine.

And the bad news for beans isn’t just a downer for coffee snobs. Climate change is expected to make a dent all across this multi-billion-dollar sector, and on the hundred million coffee farmers around the world.

But there is some hope! Researchers are looking into other coffee species that might be more resilient than Arabica and Robusta. In fact, there are 124 known wild coffee species growing across the world, from tropical Africa to Australasia.

And many are already used locally to make a morning cup of Joe. One especially promising species is Coffea stenophylla. This bean tastes similar to Arabica – and it can be grown at higher temperatures! Stenophylla and a number of other wild species have important characteristics related to heat, drought, pest and disease tolerance. Unfortunately, 60% of all wild coffee species could also be at risk of extinction.

That’s mainly because we’re destroying the forests where they are found, to make room for agriculture, livestock farming, and new settlements. In addition, some wild species are found in high-conflict regions, which presents additional challenges. So, even though many of us take for granted that coffee is a reliable part of our day, it may not be in the future. As if we needed another reason to get serious about climate change.

[Stefan]:
Who knew that lurking behind dark roast was the dark side of fungi. I guess we can't really blame them for liking the same coffee that we do. But did they have to go after bananas as well. Unfortunately, there is more flavour loss where that came from.

[Hank]:
If you like bananas, you probably eat a lot of clones. Because all bananas are clones, or at least Cavendish bananas are, and they are the cultivar, or variety, of banana that most people eat. They're genetically identical to one another.

And they are also all in danger of being wiped out by a fungus. Cultivated bananas reproduce asexually through a process known as parthenogenesis which literally means virgin birth.

 (10:00) to (12:00)


Most plants have male and female flower parts and seeds that are pollinated with the help of things like the wind or bees. Pollination is the plant version of getting it on.

And there are ways to create new banana cultivars if you pollinate them by hand but it often fails and even when it does work it's hard to know if your new banana is gonna look good, taste good, and be easy to grow. So most banana plants live a chaste life.

If you're a banana farmer you get more banana plants by cutting off a piece of the stem of an existing plant and then sticking it in the ground. That plant then matures, blooms with potentially more than 300 bananas and then dies.

Because they're all the same, they're super vulnerable to disease. There's no chance that one banana plant will happen to have a gene that makes it resistant. So if a parasite or fungus can kill one banana, it could potentially kill every banana of that type, that's something that's happened before.

Back in 2013 we here at SciShow talked about the Gros Michel banana which was bigger, sweeter, and hardier than the Cavendish went virtually extinct in the 1950s. The culprit was a highly infectious fungus we called Panama disease. In the space of about ten years Panama disease reduced the Gros Michel from the world's most popular fruit to just another weird thing your grandparents talk about but nobody else remembers.

And the banana industry would have died with the Gros Michel if it weren't for the last minute switch to the Cavendish. While it wasn't as big and didn't taste the same as the Gros Michel, the Cavendish was immune to Panama disease - at least, the type of Panama disease that was around at that time.

In 2013 we also told you that a new strain of Panama disease had emerged that could infect the Cavendish but that it would probably be fine. Infected fields were being quarantined, scientists were working on developing a new kind of Cavendish that could resist the new disease and hey, we have the lessons of history. We weren't gonna let what happened to the Gros Michel just happen again, right?

So, here’s an update on that story. According to a study published in November in the journal PLOS Pathogens this new strain of Panama disease known as Tropical Race 4 or just TR4, is spreading. It originated in Northern Australia and the last time we talked about this it was also in Southeast Asia and Southern China.

Since then, the researchers note, TR4 has reached the Middle East through Jordan and Lebanon as well as Africa through Mozambique. 

 (12:00) to (14:00)


TR4 in Africa is especially concerning because bananas in many parts of Africa, including Mozambique, are not just a tasty treat, they are a staple crop and a major component of national food security.

Even worse it seems likely that TR4 could also infect other varieties of African banana, many of which are grown as subsistence crops by rural families. What makes TR4 so dangerous? It’s caused by a fungus that spreads through soil. If you didn’t think dirt could carry disease, it can, and when it does, it’s bad.

TR4 spreads through the dirt and infects plants via their root systems. Worse, it produces chlamydospores or resting spores which can lie dormant in the soil for decades, so just destroying an infected crop won’t solve the problem. Once the soil has been infected it can’t be used for growing that kind of banana any more, at all, like maybe forever.

The only way to actually get rid of it is through fungicidal soil treatments which are so toxic and harmful to the environment that they’re prohibited pretty much everywhere. And TR4 is so infectious that even a single clump of dirt lodged in the tread of your shoes would be enough to carry the disease to a new plantation.

So far it hasn’t gotten to Central or South America which produce more bananas for export than anywhere else in the world, but it probably can’t be kept out forever. All told it’s looking more and more likely that the Cavendish is going to go the way of the Gros Michel, the questions now are, when? And will we be able to develop a new type of banana that can replace it in time? Either way, if you really like bananas you might want to enjoy them now while you still can.

[Stefan]:
So, we've seen the good and the bad when it comes to fungi from renewal to destruction. And simple fungi are behind them all because as with many symbionts a fungus's role in the world is complex. Here's how we know that a mushrooms relationship status would be it's complicated.

[Stefan from past]:
When we hear the term symbiosis, we tend to think about a partnership, like bees and flowers. The bees get nectar. The flowers get pollinated. It's a biological win-win. But when we dive into the science of symbioses, it turns out there are a couple caveats.

First off, though the term symbiosis is usually thought of as good-for-everyone, technically, it just means a close ecological relationship. It can be an everyone-wins-type situation, or a mutualism, but it definitely doesn't have to be.

 (14:00) to (16:00)


For example, parasitism is also a symbiosis, and so is commensalism, where one side is unaffected by the relationship.

Also, and most importantly for this episode, in many cases, there are more than two parties involved. And things get really interesting when you look at symbiotic threeways.

Take lichens, for instance. Often seen growing on rocks or trees, lichens are one of the classic examples of symbiosis. For 140 years, we've known that they contain both a fungus and a photosynthetic partner, like algae or bacteria. Sometimes both.

But in 2016, a team of scientists announced they'd found a new partner in the mix. They were looking at messenger RNA – the chemical "scripts" which dictate protein synthesis – from beard-like lichens. The idea was to sequence those and then work backwards to pin them to the different branches of the tree of life they came from.

You see, there had been some hints in previous studies that researchers were missing something about lichens. For instance, when they tried to grow them in sterile labs, they didn't really look  right, even when both the fungus and algae were present. In particular, a part called the cortex – a structural layer which helps transfer nutrients and water – often didn't form as expected.

Some researchers suggested that could be because there was yet another partner in the mix – something missing from those sterile environments – so the scientists hoped looking at messenger RNA could help them find it. A lot of what they got seemed to belong to the expected partners, but a few results suggested there was another fungus present.

Upon further investigation, they decided it was probably a yeast. So they took to the microscope, and sure enough, they found teeny tiny cells inside the lichen. And when they checked with other scientists, it turned out that lichens all around the world also have this yeasty partner.

The yeast is found in the cortex, that nutrient-transfering structure that was so hard to grow in the lab. It might even help build it. It may also help produce compounds like vulpinic acid, a greenish-yellow toxic pigment that may help protect the photosynthetic microbes living inside the lichen from radiation.

And the story doesn't end there. In 2019, scientists found another yeast that may be a natural component in some lichens. Making them a symbiotic 4-way!

But, for another example of a symbiotic trio, let's look at panic grass.

 (16:00) to (18:00)


Panic grasses are common throughout the world. But one especially hardy type grows near the hot springs in Yellowstone National Park, where soil temperatures can get up to 50 °C or more.

We've known for some time that this heat-tolerant panic grass has a fungal partner, and that if you break up that partnership, the grass loses its ability to grow in such hot soils. But it turns out this extreme heat resistance isn't wholly from the fungus. It's thanks to a third symbiotic partner: a virus.

Scientists were investigating this grass back in the late 2000s. They wanted to know how viruses might affect plant-fungus mutualisms, so they used a technique to look for viral genetic material inside the fungus. They detected an unknown virus infecting the fungus, and singled it out.

Normally, we'd think of a viral infection as a bad thing, but in this case, it actually seems to be an important part of mutualistic relationship between the plant and its fungus. When scientists cured the fungus of its infection and then put the newly virus-free plants in 2-week-long heat tolerance tests, they shrivelled and died, while the still-infected plants did just fine. And when fungus was re-infected, the plants regained their heat resistance.

The scientists weren't quite able to figure out how this works, but they said that it seems like the virus somehow affects the plant's stress-response system, maybe by helping the fungus eliminate damaging chemicals generated by the plant's defense mechanisms. So those are some examples of symbiosis where everyone benefits from the relationship. But remember how symbioses can be a lot more complicated?

Well, consider Bryopsis, a kind of marine algae, and their weird relationship with certain bacteria and voracious, inch-long sea slugs. Bryopsis grows in the Pacific in places like Hawaii, and both it and its predator – a kind of sea slug – use chemicals called kahalalides to defend themselves. The slugs gets these kahalalides from eating the algae.

But it turns out that the algae gets them from somewhere else, too. Specifically, symbiotic bacteria. These bacteria are found exclusively inside the algae, where they synthesize the algae's toxic defenses from compounds they get from their hosts.

These bacteria are so specialized that they can't live on their own, and about a quarter of all their messenger RNAs – those protein "scripts" we mentioned earlier – are dedicated to kahalalide synthesis. 

 (18:00) to (19:25)


The kahalalides they produce would normally keep the algae safe, but the slugs have evolved an immunity to their effects. In fact, they actually hijack these molecules for their own defenses, as well as the algae's chloroplasts.

So by eating these algae, the little grazers can transform themselves from unassuming mollusks into toxic, solar-powered slugs. Life is beautiful, man! And even though the bacteria and algae don't benefit from this because they die – they're so closely linked to the slugs that it's still considered a symbiosis.

The fact is, life is built on relationships and on webs of relationships. And these aren't even the most complex ones around. The gardens of fungus-growing ants may have five symbionts.

And even humans have symbiotic relationships with the myriad of species in our guts. So, symbiosis is complicated. It's not limited to two organisms, and not everyone wins. Which makes it all endlessly fascinating. 

[Stefan]:
And that wraps up our fungus frenzy. But if you just can't get enough of them, then boy do I have the podcast for you. On the SciShow tangents podcast we devoted an entire episode to discussing yeast, which is a fungus. And I think we ended up just as inconclusive on our stance towards them as in this compilation. But you can listen to it anywhere you get your podcasts and I hope you enjoy it.

[Outro]