Chapter 11: Plectomycetes

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Welcome to another Deep Dive.

Today, we're peeling back the layers on a kingdom of life that often goes unnoticed, yet profoundly impacts everything from the food we eat to our very health.

We're talking about fungi, specifically a remarkable group known as the plectomyces.

That's right.

Our journey today takes us into a chapter from Introduction to Fungi by John Webster and Roland Weber.

Our mission really is to transform what can be quite dense scientific information about these incredible organisms into clear, engaging insights.

We'll explore their unique structures, surprising life cycles, and their vital, sometimes hidden roles in medicine, agriculture, and biotechnology.

And all without needing a microscope, right, or a textbook nearby.

Exactly.

Think of this as your essential guide to understanding a biological kingdom far more complex and significant than you might have imagined.

From the tiny architects of disease to the silent champions in our food supply.

Yeah, get ready for some truly illuminating discoveries.

Let's dive in.

Okay, so to begin our exploration of plectomyces, we really need to understand their defining characteristic.

It's all about how they form their asset.

The spore -bearing sacs, yeah.

Precisely.

Unlike many fungi where these structures are, you know, openly exposed, plectomyces primarily produce them within a completely enclosed spherical casing called a clistothesium.

Okay, clistothesium.

So like a tiny sealed case, protecting the spores inside.

Exactly.

Imagine that.

Although sometimes you'll find an open cage -like construction, which they call a gymnothesium, still interwoven, but allows for a bit more air movement.

Interesting.

And while, you know, advanced DNA analysis has shown a few evolutionary exceptions, this enclosed or semi -enclosed structure is actually a surprisingly good indicator of their evolutionary relationships.

So if we could shrink down, observe these fungi up close,

what are some of the key visual traits?

What would stand out?

Well, under high magnification, you wouldn't see the assae neatly lined up in a specific layer like you might in some other fungi.

Instead, they're typically scattered randomly throughout that clistothesium or gymnothesium.

Just dotted around.

Yeah.

And each ascus is generally globose, sort of spherical and very thin -walled.

The ascus spores themselves, the sexual spores, they're quite small, often spherical or maybe oafle.

And how do they get out?

Ah, well, what's particularly distinctive is their release.

It's entirely passive,

meaning the ascus wall just disintegrates, it breaks down, and the spores are just there, waiting to be dispersed.

There's no active shooting mechanism like you see in some other fungi.

Huh.

No little cannons firing spores out?

Nope, none of that.

And beyond these sexual spores, they also commonly produce canidia.

Those are the asexual spores, often from specialized flask -shaped cells called phyleids, or sometimes as arthrocannidia, which when bits of the fungal hyphae just sort of break off into chains of spores.

Okay, so we've got a picture of their microscopic anatomy.

Panyspheres, passive release, asexual options.

But what does this mean for their actual lives, you know, in the bigger world?

What's their ecological footprint?

That's a crucial question.

Many plectomycetes are predominantly saprotrophic.

Saprotrophic, meaning they live on dead stuff.

Exactly.

They live by breaking down and feeding on organic matter, especially common in soils.

And here's where their real power becomes evident.

They possess a remarkable capacity to degrade incredibly tough biopolymers.

Like what kind of tough stuff?

Well, we're talking about complex carbohydrates like starch and cellulose, you know, the stuff that makes up plant cell walls, and even robust proteins like keratin.

Keratin, like in hair, horns, feathers.

Precisely.

This isn't just a biological detail.

It means these fungi are the unsung heroes of decomposition,

tirelessly recycling vital nutrients, basically stopping the planet from being buried under its own waste.

Wow.

So these are the ultimate recyclers, cleaning up the natural world.

That's a truly powerful ability.

It is.

It really is.

But this very efficiency, it comes with a surprising twist.

If these highly proteolytic fungi, the protein -breaking ones, can also thrive at human body temperature, which is about 37 degrees C.

Uh -oh.

I see where this might be going.

Yeah.

They suddenly become potential pathogens.

In fact, some of them are among the most dangerous fungal pathogens to humans, and they don't just break things down.

They also produce important secondary metabolites.

Secondary metabolites, meaning chemicals not essential for their basic growth.

Exactly.

Chemical compounds that can be incredibly useful to us, like valuable antibiotics or, unfortunately, highly harmful mycotoxins.

Quite a dual nature they possess.

Wow.

Okay.

The text highlights three main orders within the plectomycetes, eschospherals, oneginales, and urotials.

Let's delve into the eschospherals first.

Right.

This is a relatively small order, but it stands out because of its unusual habitats.

They're largely associated with beehives or act as problematic food spoilage fungi.

Interesting.

Yeah, and many require very specific substrates, rich in sugar or salt.

Some are truly xerophilic.

Xerophilic, meaning dry -loving.

Exactly.

They can grow in extremely dry conditions, thanks to something like a 60 % glucose solution, which is incredibly concentrated.

Wow.

That's extreme.

It is.

And interestingly, even though they don't produce those characteristic true clastathecia,

DNA studies firmly place them within this group, showing their evolutionary connection.

What are some examples of the practical impact?

You mentioned food spoilage.

Well, take aromascus, for instance.

This is a common food spoilage fungus, often found lurking on moldy jam or even in powdered mustard.

Moldy jam.

Yep.

Seen that.

It's an interesting exception to the rule because its asses aren't organized into a fruiting body at all.

They're just sort of free -floating.

And aromascus is also homotholic.

Meaning it can self -fertilize.

Right.

Which makes spore dispersal pretty straightforward for it.

Just passive release.

Okay.

And then there's their connection to bees, which sounds,

frankly, a bit more serious.

Indeed.

Ascosfera apis.

This is the culprit behind what's known as choc brood disease in honeybees.

Choc brood.

Why choc?

Because when the larvae get infected, they literally appear white and hard, like tiny pieces of choc, and eventually dark spore balls can actually burst through their skin.

Yikes.

That sounds awful.

It can be devastating, seriously weakening bee colonies, especially when they're already dealing with other stresses like the varro mite.

That sounds like a serious threat to our essential pollinators.

How do bee colonies, as a whole, cope with this fungal invasion?

Well, ascosfera apis is heterothalic.

Meaning it needs two different partners,

correct.

Needs two mating types to produce those infectious spores.

It forms a structure called a sporicist.

It's a unique spore -containing body, but not technically a true clistothesium.

Okay.

And the fungus itself thrives at around 30 degrees C.

Now that's actually a bit cooler than the normal hive temperature, which is usually 33, 36 degrees C.

So the bee's normal temperature is slightly protective.

It seems so.

And here's a fascinating insight into bee behavior.

Colonies have evolved remarkable responses, like behavioral fever.

Behavioral fever?

What's that?

The worker bees collectively work to elevate the hive temperature, making it less hospitable for the fungus, trying to retard the disease's growth.

Wow.

They heat the hive up on purpose.

Seems like it.

They also practice incredible hygiene, meticulously removing any dead larvae before the fungus can sporulate and spread its spores everywhere.

Smart bees.

Very.

And perhaps surprisingly, viable aapis spores can even be found sometimes in commercially available honey.

Doesn't mean it's harmful to us, but it shows how persistent they are.

Right.

Okay, moving on then.

The next order, the onigenales.

You said this one is particularly important medically.

Profoundly important, yes.

Especially for medical mycologists, this group contains most of the true human pathogens.

True pathogens meaning they can cause disease even in healthy people, not just those with weakened immune systems.

Exactly.

These are fungi capable of causing disease even in otherwise healthy individuals.

Okay, this sounds like where the stakes get really high for us.

What makes them such effective pathogens?

How do they actually work to cause disease?

Well, a defining characteristic of onigenales is their ascoma, which is usually a gymnathesium.

The cage -like one, not the sealed one.

Right.

Unlike the completely closed clostathesium, this is a loosely interwoven, often thick -walled hyphal structure.

And these can have complex, often kind of bristly, appendages.

Appendages.

For what?

Well, research suggests these cage -like structures and their appendages might actually be an evolutionary adaptation for dispersal by arthropods, like flies.

Flies spreading fungus.

How?

The idea is they might brush against them, shake out the spores.

The assy inside are typically spored and evanescent, meaning they disappear quickly, releasing spores passively.

Okay.

And where do these fungi live normally?

Most species in this order are found in the soil, and they're often associated with keratin -containing substrates.

Ah, keratin again.

Hair, hooves, feathers.

Exactly.

That seems to be their niche.

The text singles out four particularly dangerous human pathogens in this group.

Can you shed some light on them?

Absolutely.

These are fungi usually known by their asexual or anamorphic names.

You've got histoplasma, capsulatum, blastomyces dermatitis, paracuchidioes, brasiliensis, and cotidioides amytis.

Right.

Those sound serious.

They are.

They're so hazardous that they are classified as hazard category three organisms.

Strip containment is required, and they're generally not permitted in standard teaching labs, for example.

Wow.

Okay.

So what do these four have in common?

Several key features.

First, it's important to that while they cause disease in humans, they are primarily sepertrophic in the soil.

So decomposers first and foremost.

Right.

Their ability to cause human disease is actually thought to be quite coincidental.

It's driven by their natural efficiency at breaking down organic matter, coupled with their ability to grow well at 37 degrees C, evade our immune system, bind to human tissue, and produce proteases, those protein -digesting enzymes.

And how do people get infected?

Almost always by inhaling tiny asexual spores called microconidia from disturbed soil.

These are small enough to get really deep into the lungs, into the alveoli.

And then what happens?

And then they transform into their disease -causing yeast -like stages.

Or for coquidioides amytis, they form unique structures called spirals.

This transformation is key.

And you mentioned temperature.

Yes.

Second key feature.

All of them are dimorphic.

This is critical.

They switch forms depending on temperature.

Dimorphic two forms.

Exactly.

At cooler temperatures, maybe 27 degrees C, like in the soil, they grow as filamentous hyphae, like typical mold.

But at human body temperature, 37 degrees C, they transform into that yeast -like form, or spirals.

That's their pathogenic phase.

And often just the temperature shift itself is enough to trigger the change.

That's amazing.

What kind of illness do they cause?

Well, third point,

the pulmonary infections can vary widely.

Sometimes it's just mild flu -like symptoms that might go unnoticed.

Other times it can be severe, even resembling tuberculosis.

And can it spread?

Yes.

In serious cases, they can spread systemically to other organs.

However, in milder cases, patients often recover and, importantly, gain lifelong immunity.

Lifelong immunity.

That sounds promising for vaccines.

Exactly.

That's a significant factor driving research into vaccine development for these diseases.

Okay.

What else?

Fourth, and this is truly fascinating, these fungi have evolved ways to survive and even reproduce inside the very immune cells meant to destroy them, our macrophages.

Inside our immune cells.

How?

They do it by cleverly raising the internal pH of the macrophage, making it less acidic, and resisting the lolitic enzymes that would normally break them down.

Wow.

Talk about adaptation.

It's incredible.

And these internal yeast cells can act as a kind of latent inoculum, lying dormant for potentially years and then causing relapses later on, much like the bacteria that cause tuberculosis.

That's scary.

How are they treated?

Fifth point.

Treatment usually involves prolonged chemotherapy with potent antifungal drugs like amphotericin B and various azole type compounds.

But these often come with problematic side effects.

Right.

Newer drugs like caspifungin are showing some promise, thankfully.

And you mentioned something about men and women.

Yes.

Finally, a really surprising epidemiological detail.

Diseases caused by all four of these fungi are much, much more prevalent in men than in women, often by a ratio of 10 to 1 or even higher.

10 to 1.

Why?

It appears to be due to the inhibitory effects of the hormone estrogen on that crucial transition from the spore form, the knidium, to the pathogenic yeast form.

Wow.

So hormones actually play a role in resistance.

That's a profound detail.

Are there any particular memorable details about each specific pathogen?

Absolutely.

Histoplasma capsulatum is famously linked to Spelunker's disease.

Cave explorer's disease.

Exactly.

Because infection often results from inhaling spores found in bird or bat droppings, often accumulating in caves or old buildings.

Pericotudioids brasiliensis is visually striking in its yeast state at 37 degrees stea.

It forms a large central cell and several smaller daughter cells bud off it, creating this really distinctive pilot wheel stage.

You can spot it under the microscope.

Pilot wheel.

And cuttiduites imidus is well known for causing valley fever, especially common in arid regions of the southwestern U .S.

after soil disturbances, like dust storms or construction, kick up spores.

Valley fever, right.

Heard of that.

And what's noteworthy here is that, despite no known sexual form ever being observed, DNA evidence strongly suggests that sexual recombination does occur naturally for this species out in the environment.

They're mixing genes somehow.

Hidden reproduction.

Fascinating.

Okay, beyond these major human pathogens, what else do we find lurking in the onigenals?

Well, we find onigena.

This is an unusual keratin -degrading fungus found on things like animal hair, horns, and feathers, usually after the animal is dead.

More keratin eaters.

Yep.

It forms a unique stalked ascostroma, like a fruiting body on a little stalk that ruptures to expose its spores.

And interestingly, it produces a distinct cadaverous smell.

A bad smell.

Why?

The suggestion is it might attract carrion flies for dispersal, making it one of the few known insect dispersed fungi.

Clever.

If a big grim.

What else?

Then there are the arthrodermataceae, collectively known as dermatophytes.

Dermatophytes.

Sounds familiar.

It should.

These are the fungi responsible for common ringworm or teeny infections on our skin, hair, and nails.

Ah, ringworm, athlete's foot, nail fungus.

That group.

Exactly.

They are keratinolytic, meaning they specialize in degrading the keratin in those tissues.

Fortunately, these infections are typically confined to the outer, dead layers of our skin and are generally relatively easy to treat compared to the systemic ones we just discussed.

Right.

This raises an important historical question.

How do we first figure out that these specific fungi were causing these, you know, common skin diseases?

Uh, well, this family holds significant historical importance in medical mycology.

Way back in 1842, a pioneering researcher named Robert Remack famously infected himself experimentally.

He infected himself on purpose.

He did.

With a fungus now known as trichophyton shunlaini to definitively prove its pathogenic role in a scalp condition called faevis, a brave move for science.

Definitely.

Later, Raymond Saburod revolutionized the field.

He pioneered methods to identify different dermatophytes based on their distinct appearance when grown in laboratory cultures.

Many of his techniques are still foundational today.

And how do people usually get these?

Transmission is quite common.

Often from pets like trichophyton viruicosum from cows can cause ringworm, or through communal facilities like showers or locker rooms, which is how athlete's foot often spreads.

Right.

Makes sense.

Any other groups in Oniginellus?

We also encounter the gymnoascesi.

These are mainly saprotrophic soil fungi, again degrading keratin and also cellulose.

They often produce strikingly colored gymnothesia, those cage -like structures, especially noticeable on herbivore dung.

Colorful fungi on dung.

Okay.

And finally, the myxotrichesia.

These include the cellulolitic myxotrichum charterum, which is notorious for causing paper spoilage.

If you've ever seen old books with fuzzy mold, this could be the culprit.

Ruining old books.

The horror.

Indeed.

Its precise taxonomic position is still a bit debated, actually.

Some studies suggest it might belong to a different order entirely, possibly showing a fascinating example of convergent evolution, where different groups independently evolved a similar structure, the gymnothesium.

Convergent evolution.

So similar solutions to similar problems, even if unrelated.

Cool.

All right.

Let's turn our attention now to the urotials.

This is a group that, frankly, many of us probably interact with every single day, often without even realizing it.

This order includes the really famous ones, right?

Aspergillus and penicillium.

You've absolutely hit on a critical point there.

The urotials are, you could argue, among the most important groups of fungi in practical mycology.

They are truly ubiquitous.

Ubiquitous meaning everywhere.

Pretty much.

Found in virtually every soil sample, water source, floating in the air around us, often appearing as contaminants on our fad.

A key feature, like some ascospherales, is that many are highly xerophilic.

Are I loving again?

Yep.

They can grow even in very dry conditions.

This makes them major culprits in food spoilage on things like stored cereals, nuts, jams, dried fruit, anywhere with low water activity.

Right.

So how do we distinguish these microscopic powerhouses from each other?

If we had that powerful microscope, what visual cues might we look for?

Microscopically, they're canadiophores.

Those structures that bear the asexual spores are quite distinctive.

They have unique branching patterns, almost like fungal fingerprints.

In Aspergillus, the tip of the canadiophore swells up into a structure called a vesicle, almost like a tiny balloon head.

And the spores, the canidia, radiate out from it either directly or from little stalks on the vesicle.

Little spore -hitted structure.

Kind of, yeah.

Penicillium, on the other hand, doesn't have that swollen vesicle.

Instead, its canadiophore branches repeatedly, forming a structure that looks remarkably like a miniature brush.

Hence the name, from penicillus, Latin for painter's brush.

The spores form in chains off the bristles.

Okay.

Aspergillus, like a head.

Penicillium, like a brush.

Got it.

Exactly.

And the process of canadian formation itself is incredibly efficient.

From a fixed point on a specialized cell, the phialide, it just keeps churning out a chain of canidia one after another, each new spore forming its own wall.

Like a little spore factory.

Pretty much the entire cycle from a single spore germinating, growing hyphae, and then producing a whole new crop of millions of canidia can take as little as 24 hours in some species.

Wow, 24 hours.

That rapid turnaround time certainly explains their omnipresence.

Yeah.

They just pop up everywhere.

It absolutely does.

That speed and efficiency are key to their success.

So what are these incredibly adaptable fungi doing for us, and sometimes unfortunately to us, in the real world?

They are, without exaggeration, biotechnological superstars, arguably second only in importance to baker's yeast, saccharomyces cerevisiae.

Let's start with the good stuff.

Okay, hit me with the good news first.

Right.

In food production, aspergillus species have been used for centuries, especially in the Far East, for processes like brewing sake from race starch, and crucially in the koji process for making soy sauce.

Koji, what's that?

Koji is basically steamed grains, usually rice or soybeans, inoculated with specific aspergillus species.

These fungi produce enzymes that efficiently break down the starches and proteins in the grains.

For soy sauce, they break down soybeans and wheat, which is essential for its flavor development.

So we've been using aspergillus intentionally for food for ages.

For millennia.

And what's truly fascinating here is that the aspergillus areza and aspergillus soje used in soy sauce appear to be domesticated forms of aspergillus flavus and aspergillus parasiticus.

Wait, aren't flavus and parasiticus the ones that produce dangerous toxins?

They are.

They're notorious for producing potent mycotoxins, aflatoxins specifically.

So it seems humans somehow selected or modified strains that lost their toxicity but kept their powerful enzymatic abilities.

An incredible example of early biotechnology, really.

That is amazing.

Domestication of a mold.

Pretty much.

And of course, let's not forget penicillium species, like penicillium roqueforti for roquefort and other blue cheeses, and penicillium camemberti for camber and brie.

They're absolutely vital for producing those beloved cheeses, contributing significantly to their unique flavors and textures through lipolysis and proteolysis.

Cheese.

Okay.

Good uses so far.

What else?

Beyond food, aspergillus species produce the vast majority of all commercial fungal enzymes.

These enzymes are used in countless industries.

Dairy, baking, brewing, fruit juice clarification, even in textile and leather manufacturing to soften fabrics or prepare hides.

They're industrial workhorses.

Enzymes for everything.

Almost.

And aspergillus niger has been the world's most important producer of citric acid since way back in 1923.

It churns out an astonishing 9 million tons annually.

9 million tons of citric acid from a fungus.

Yep.

It's an incredibly efficient fermentation process, converting up to 95 % of the sugar fed to it directly into citric acid, even though the exact biochemistry behind why it accumulates so much citric acid is still not fully completely understood.

Still a bit of a mystery, but it works incredibly well.

Precisely.

And then, of course, there's the legendary story of penicillin.

What are the fungal details behind that world -changing discovery?

Ah, penicillin.

It's one of the most famous accidents in science, isn't it?

Alexander Fleming, in 1928, noticing that a contaminating mold, penicillium notatum, was inhibiting the growth of his bacterial cultures on a petri dish.

The mold juice discovery.

Essentially, yes.

But the real triumph was its later development into a life -saving antibiotic by Howard Flory, Ernst Chain, and their team at Oxford during World War II.

A truly monumental achievement for human history.

Absolutely.

And we still use it today.

We use derivatives, and the production of penicillin strains have been massively improved.

Today, commercial production typically uses penicillium crizzorundum.

Through decades of mutation and selection, scientists have enhanced yields an incredible 50 ,000 -fold from Fleming's original strain.

Just amazing scientific innovation.

50 ,000 times more potent.

Wow.

And this group, the Urochialis, also produces other important antibiotics, like the chemically related cephalosporins, and also crucial antifungal drugs like grizofulvin, which is used to treat those dermatophyte infections we talked about earlier.

Okay.

So foods, enzymes, world -changing antibiotics.

Yeah.

Quite the resume.

But you mentioned a darker side earlier.

Yes.

As impactful as these beneficial applications are, it's critical to acknowledge the flip side.

Many members of Aspergillus and penicillium are notorious for producing highly toxic chemical compounds called mycotoxins.

Mycotoxins.

I'll call them toxins.

Exactly.

And they pose a major health hazard, especially when they contaminate our food supply.

Like which ones?

Well, consider aflatoxins, produced mainly by Aspergillus flavus and Aspergillus parasiticus.

These are among the most potent, naturally occurring carcinogens known.

Carcinogens.

Cancer -causing.

Extremely potent liver carcinogens, capable of inducing cancer at incredibly low concentrations.

They came to notoriety with the infamous Turkey X disease outbreak in the UK back in 1960, where thousands of turkeys died from contaminated peanut meal.

That event really spurred global research into mycotoxins.

And where do we find aflatoxins now?

They can commonly contaminate crops like corn, peanuts, cotton seed, tree nuts, and spices, especially if storage conditions are warm and humid.

Strict regulations exist in many countries, but it's an ongoing challenge.

Okay.

Aflatoxins.

What else?

Then there's ochratoxin A.

This one is produced by numerous Aspergillus species, but also some penicillium species.

It's primarily nephrotoxin.

Meaning it harms the kidneys.

Yes.

It's been strongly implicated in a severe human kidney disease called Balkan endemic nephropathy, found in certain regions of southeastern Europe.

It's also suspected of causing other cancers, like pig blood or cancer.

And worryingly, it has a remarkably long residence time in the human body, meaning it sticks around.

Not good.

Any others?

And patchelin.

This one comes from penicillium expansum, which is the fungus that causes the common brown rot of apples.

The moldy apple fungus.

Exactly.

Patchelin is frequently detected in apple juices and other apple products, especially if made from damaged or moldy fruit.

It's also considered a potential carcinogen and is regulated in many places.

Right.

So toxins are a major concern.

What about direct infections caused by these fungi, not just their chemical byproducts?

Yes.

Direct infections or mycosis are also a significant concern, especially with Aspergillus.

Aspergillus species, primarily Aspergillus fumigatus, and again, Aspergillus flavus, are common causes of these infections.

How do these infections usually happen?

Well, in patients with healthy immune systems, inhaling Aspergillus spores might lead to allergic reactions, or sometimes they might form non -spreading fungus balls, called Aspergillomas, usually inside pre -existing lung cavities, like from old TV scars.

They just sort of sit there.

Okay, but what about people with weakened immunity?

That's where it gets really dangerous.

In immunocompromised individuals, think transplant recipients, cancer patients on chemotherapy,

people with advanced AIDS Aspergillus, can cause invasive Aspergillosis.

The fungus actually invades lung tissue and can spread through the bloodstream to other organs like the brain.

This can be rapidly progressive and often fatal, unfortunately.

That sounds terrifying.

Why is Aspergillus fumigatus such a common culprit?

Several reasons.

Its canidia are incredibly small and lightweight, so they're easily aerosolized and constantly inhaled by pretty much everyone, and crucially, it's highly thermotolerant.

Thermotolerant, like seed.

Loves heat.

It thrives in temperatures up to 50 degrees C or even higher, which is unusual for many fungi.

You find it growing abundantly in hot environments, like compost heaps and decaying vegetation.

This heat tolerance means it grows perfectly well at our body temperature of 37 degrees C, giving it a major advantage once it gets into our lungs.

It's an ever -present environmental threat.

Always around.

Loves heat, tiny spores.

A difficult combination.

Any other infectious ones in this group?

There's a unique case.

Penicillium marnife, now renamed Talaromyces marnife, but historically known as a penicillium.

It's unique because it's the only species in this lineage that's dimorphic, like those oniginales pathogens we discussed.

So it switches from hyphae to yeast at 37 degrees C.

Exactly.

It causes serious systemic infections, primarily in Southeast Asia.

Tragically, the incidence of these infections dramatically increased with the spread of the AIDS epidemic in that region, as it primarily affects immunocompromised individuals.

Right.

It sounds like the urotials are a group of fungi with just immense impact, both incredibly positive and dangerously negative.

What about some of the lesser -known, perhaps more hidden members of this group?

Anything else interesting?

Absolutely.

There's the family Elaphomycetaceae, often commonly called Hertz truffles or deer truffles.

Hertz truffles?

Are they like the edible truffles?

Not quite the culinary ones, no.

These are hypogeus, meaning they grow entirely underground, but they're not closely related to the gourmet truffles like tubers.

Okay, so underground fungi, what do they do?

They form ectomycorazole associations, that's a symbiotic relationship, on the roots of trees, particularly trees like beech and oak.

And they are actually an important part of the winter diet for animals like squirrels and deer who dig them up.

Ah, so food for wildlife.

Exactly.

Their fruit bodies are regarded as true Cleistothacia, those closed sacs again, often with a thick, distinct two -layered rind and the typical globos assai scattered inside.

And interestingly, for these particular fungi, there are no known asexual or anamorphic states ever found.

They seem to rely entirely on sexual reproduction.

Only sexual spores for the deer truffles.

Now, one of the most intriguing aspects of the Orocheles, and frankly, fungal evolution and taxonomy in general, especially when we talk about aspergillus and penicillium, is the sheer number of species for which no sexual state has ever been found.

Really?

How many are we talking about?

It's a huge percentage.

Over 60 % of known aspergillus species and about 31 % of penicillium species have only ever been observed reproducing asexually via knidia.

Wow, that's a massive number.

What's the scientific implication of so many species seemingly missing sexual reproduction?

Has it just not been found yet or did they lose it?

It's a really compelling puzzle.

The leading hypothesis is that the ability to reproduce sexually has actually been lost independently on many separate occasions throughout their evolution and perhaps quite recently in evolutionary terms for some lineages.

Lost the ability.

How can we tell?

Well, we see these tantalizing hints.

Some purely asexual species still produce sterile structures that look remarkably similar to the tissues that would normally surround a clistothesium in their sexual relatives.

It's as if they carry these vestiges, these remnants of a lost sexual past.

Like evolutionary echoes.

Exactly.

And this raises a profound evolutionary question.

Are these purely asexual species perhaps more vulnerable to extinction over long periods?

Why would they be?

Because they accumulate harmful mutations over time without the benefit of genetic recombination that sexual reproduction provides.

Meiosis shuffles the genetic deck, potentially purging bad mutations or combining good ones.

Asexual lineages just keep copying their genome errors and all.

So sex is important for long -term adaptability and purging errors.

Makes sense.

It does.

And these complexities also really highlight the challenges in classifying these fungi.

For example, you have genera like Eurotium and Emericella.

These are teleomorphic genera.

Telemorph meaning the sexual stage.

Correct.

They represent the sexual forms, the ones that make clistothesia.

And crucially, both Eurotium and Emericella have aspergillus species as their anamorphs, their asexual stages.

So one fungus, two names, depending on whether it is reproducing sexually or asexual.

That sounds confusing.

It historically was, though mycologists now strive for a one fungus, one name system based on DNA.

But these connections show the relationships.

Eurotium, for example, is often the genus you find making little yellow clistothesia and moldy jam.

Emericella is different.

Its ascocarp, the sexual structure, is enclosed by distinctive, thick -walled sterile cells called Hull cells.

Hull cells?

Yeah, unique protective cells.

And its ascospores are really cool looking.

They have a prominent double equatorial flange, like two ridges around the middle, making them resemble tiny pulley wheels.

Pulley wheel spores.

Amazing detail.

It is.

These examples just beautifully illustrate the incredible diversity hidden within these groups and the ongoing challenges, but also the real excitement in unraveling fungal taxonomy and evolution using both morphology and modern genetics.

It really sounds like a dynamic field.

Absolutely.

As we conclude this deep dive, it's just abundantly clear that the plectomycetes are an incredibly diverse and seriously impactful group of fungi.

Yeah, from being hidden away as vital soil saprotrophs, tirelessly breaking down the tough stuff.

Right.

To their surprising dual roles as, on one hand, dangerous human pathogens, and on the other, invaluable industrial powerhouses in food production and medicine.

And even providing essential food for wildlife, like those deer truffles.

Their influence is truly pervasive, isn't it?

It really is.

All around us, often unseen.

So what insight, or maybe surprising fact, stands out most to you from this journey into the plectomycetes today?

I think for me, it's that duality.

How the same group can hold something like penicillium crizogenum, the source of penicillin that saved millions, and aspergillus flavus, making one of the most potent carcinogens known.

It just highlights the incredible chemical creativity of fungi and how fine the line can be between benefit and harm.

Yeah, that chemical creativity is astounding.

Perhaps the next time you, our listener, spot a bit of mold on an old jam jar, or maybe hear about a new antibiotic development, you'll think of the tiny, incredibly complex world of fungi behind it, constantly shaping our environment and our lives in ways we're really just beginning to fully understand.

Thank you so much for joining us on The Deep Top.