Chapter 7: Zygomycota

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Fungi.

They're everywhere, right?

Yeah.

I mean, from the mold on that bread you forgot about to these huge hidden networks under forest floors.

Absolutely everywhere.

But today,

we're really zeroing in on one specific group, an ancient and well -often overlooked group, the zygomycota.

That's right.

They hold some truly surprising secrets.

And their impact, you know, from the tiniest scale up to the macroscopic world, it's way more profound than you might think.

So let's unpack this a bit.

We're diving deep into zygomycota today.

Our main guide is chapter seven of Introduction to Fungi.

A classic text.

Yeah.

And our mission, really, is to cut through some of the, let's face it, dense science and give you a clear kind of engaging picture of these organisms.

Makes sense.

We'll look at their unique shapes, their incredible life cycles, and the vital roles they play, sometimes hidden in ecosystems and even in human tech and health.

Get ready for some aha moments, hopefully.

Exactly.

Okay.

First things first.

What exactly are zygomycota?

Well, a big headline is no modal stage.

Meaning no swimming spores.

None at all.

Instead, for asexual reproduction, they rely on these non -motal spores, basically tiny immobile units.

They're called aplanospores.

Aplanospores.

And they're often produced inside these little sac -like structures.

Sporangia.

Right.

Sporangia.

Yeah.

And dispersal.

You said no swimming.

Usually passive, you know, wind, insects carrying them, maybe rain splash, though, as we'll get to, sometimes it's anything but passive.

Intriguing.

What about sexual reproduction?

Equally unique.

It results in this really resistant, thick -walled structure called a zygospore.

Zygospore.

Got it.

Yeah.

And inside, what's their structure like?

It's pretty interesting.

They have what's called a coenocytic mycelium.

Kind of acidic.

Yeah.

Think of it like one huge continuous cell, like a big bag with loads of nuclei all floating around in the same cytoplasm.

No cross walls or very few.

Wow, okay.

One big cell network.

Essentially.

And they're cell walls.

Made of chitin and chitosan.

Typical fungal stuff, but the proportion is characteristic.

Chitin and chitosan.

Now, what's really fascinating is where they sit on the fungal family tree.

Molecular data suggests they branched off from the chytridiomycota really early.

We're talking early in the history of life on land.

Wow, ancient then.

Very ancient.

And crucially, if you look at the bigger evolutionary picture, the zygomycota probably gave rise to the ascomycota and basidiomycota.

You mean like the higher fungi.

Mushrooms, yeasts, that sort of thing.

Exactly.

So zygomycota are basically the ancestors, the ancient forebears of many fungi you'd recognize.

That's fundamental.

So how are they classified now?

Broadly, there are two main classes.

You've got the zygomycetes with maybe 870 species or so.

Okay.

And the trichomycetes with over 200 species.

Right.

And within the zygomycetes.

Key groups.

Oh, yeah.

There are a few really prominent orders.

You've got the mucerales.

They're super common in soil.

Dung.

Mostly decomposers, though some can be parasitic.

Mucerales.

Okay.

Soil and dung.

Then there are the entomophthorales.

That's a fascinating bunch.

Includes a lot of insect parasites.

Insect parasites, right.

And finally, the glomales.

Hugely important.

They form these vital mutual relationships with plants.

We'll definitely talk more about them.

Okay.

Mucerales, entomophthorales, glomales.

Let's maybe focus on the mucerales first.

They sound like a good starting point.

Absolutely.

They show off a lot of the key zygomycete features.

Asexualy, like we said, they typically make loads of spores inside those round sporangia.

Sometimes the sporangia are smaller, maybe with fewer spores, and they're called sporangiola.

Sporangiola.

Or the spores might be lined up in a single row inside a kind of cylindrical sack.

That's a merosporangium.

Different ways to package spores.

Different strategy.

Exactly.

And here's a little detail for anyone studying this stuff.

When a sporangiospor from this group germinates, it actually lays down a new wall inside its original spore wall.

It's a subtle difference from what some people might call canidia in this group.

Ah, okay.

An internal new wall.

Yeah.

Interesting.

So these mucerales, these are decomposers.

They are champions of decomposition, yeah.

Really important in the first wave of breaking down dead stuff.

But not always helpful.

You mentioned parasites earlier.

Right.

They're not always benign.

Rhizopistilonifer, for example, that's the classic black bread mold.

But it also causes serious soft rot in fruits like apples, strawberries, a big cause of food spoilage.

Yeah, I think I've seen that.

And more seriously, some species can cause diseases in animals and in humans too, especially people with weakened immune systems.

It's called mucormycosis.

Mucormycosis.

Okay, so potentially dangerous then.

It can be, yes.

But that raises the question, are they all bad news when they're not busy decomposing?

Good question.

And the answer is definitely no.

Quite a few mucerales species are actually crucial in making traditional Asian foods.

Think sufu, which is fermented tofu, or tempeh, fermented soybeans.

Oh, really?

I didn't know fungi like this were involved in tempeh.

Yep.

Some are also used as starters in the saccharification, breaking down starches into sugars, which is a key step for making alcohol.

So food and fermentation.

And modern biotech too.

Many are used in biotransformation using the fungus' metabolism to change one chemical into another, more valuable one.

Okay.

And what's really cool here is that some mucerales are oleaginous.

Oleaginous means oily.

Exactly.

They can make and store large amounts of lipids, oils, and some of these include valuable polyunsaturated fatty acids, PUFAs.

Huge interest in biotech for those biofuels, nutritional supplements, you name it.

Wow.

From food spoilage to valuable oils?

That's quite a range.

Yeah.

Okay.

Let's switch gears slightly.

How do they grow and react to their environment?

Well, many mucerales have this coarse, really richly branched mycelium, that network of threads, and some, like mucoruxi, show this cool thing called dimorphism.

Dimorphism.

Two forms.

Yeah.

They can switch between that normal thread -like filamentous growth and a single -celled yeast -like form.

They often do this when oxygen is low under anaerobic conditions.

So they can adapt their shape to the environment.

Precisely.

It lets them thrive in different spots like oxygen -rich soil or an anaerobic fermentation tank.

Very flexible.

That is flexible.

Any other amazing growth examples?

Oh, absolutely.

This is where it gets really interesting with a fungus called Phycomyces blaxellianus.

Phycomyces.

Okay.

Imagine a single, huge cylindrical hypha, one single tube growing straight up, maybe several centimeters tall.

Just one giant strand.

Yeah, it's the sporangy 4, the stalk holding the sporangium.

And this thing is incredibly sensitive.

Sensitive how?

To light, obviously, but also gravity, physical stretch.

It even has an avoidance response if it grows near a solid object.

Avoids things.

How?

Well, we think it senses changes in volatile gases around it.

But the light response is amazing.

It acts like a tiny cylindrical lens, focusing light onto the side away from the light source.

Okay.

And that focused light somehow inhibits growth on that far side, causing the whole thing to bend toward the light.

It's incredibly precise.

It can respond to light as dim as starlight.

Starlight, that's unbelievable sensitivity.

It really is.

And get this, as this sporangy 4 grows upwards, it actually rotates.

Rotates like twists.

Yeah, it goes through phases, clockwise rotation, then it stops, then anticlockwise, then back again.

Why would it do that?

Well, the exact reasons aren't totally pinned down.

It might be linked to how the Keaton microflaborals, the building blocks in its wall, are laid down in a spiral.

Or maybe it's just a passive result of the internal water pressure, the turgor.

Huh.

Still figuring that one out.

Yeah.

Here's another weird thing.

If you snip off the mature sporangium at the top,

the stalk stops growing.

But if you carefully put it back on, it starts growing again.

No way!

Like the spores are sending a signal.

It seems like it.

Almost as if the spores are making some kind of growth hormone.

It reminds me a bit of apical dominance in plants, you know, where the top bud controls the side branches.

That's fascinating.

Really sophisticated development.

Absolutely.

And inside that sporangium, things are busy.

Nuclei are dividing like mad, and then the cytoplasm starts cleaving, using special membranes to package each nucleus into an individual spore.

And you can get a lot of spores in one go.

A staggering amount.

Phycomyces, the one we were just talking about, can produce up to 100 ,000 spores in a single sporangium.

Wow.

That's maximizing your chances.

Definitely a numbers game for dispersal.

And another little defense mechanism.

Some sporangial walls have calcium oxalate crystals embedded in them.

Crystals?

What for?

Gives them a spiny surface.

The idea is it probably deters tiny arthropods, like mites, from eating them.

Clever.

Like tiny little defenses.

Exactly.

And getting those spores out, spore liberation, it's not just one method either.

In many common mucor species, the sporangium wall just kind of dissolves.

It turns into this slimy blob, a sporangial drop, that sticks to the central column bit, the columnella.

And how do those get around?

Sticky spores are great for catching a ride on insects, or getting splashed around by rain.

Makes sense.

Insect or water dispersal.

But then you have others, like mucor plumeus, where the sporangial wall actually shatters and breaks into pieces.

Ah, so dry spores then.

Yep.

Allowing dry spores to be easily picked up and carried off by air currents.

Different strategy for wind dispersal.

So switching from asexual spores, what about sex?

You mentioned zygospores earlier.

Right.

Sexual reproduction in mucerales.

It happens through something called gametanjole conjugation.

Gametanjole conjugation, okay.

Basically specialized branches from compatible mycelium meat fuse.

And that leads to the formation of those really tough, thick -walled zygospores.

And compatibility.

Are they self -fertile?

Some are, yeah.

Those are called homothallic.

A single spore can grow into a mycelium that eventually forms zygospores all by itself.

But not all.

No, the majority are heterothallic.

They need two different compatible mating types.

Think of them like sexes, but they're just called plus and fiend.

Plus and minus strains, okay.

And these two compatible mycelia have to find each other, grow towards each other, make contact, fuse.

Then they form the zygospores.

How do they find each other?

Is it random?

No, it's like a chemical conversation happening underground.

Chemical conversation.

Yeah, the whole mating process is controlled by hormones.

Specifically, a family of molecules called trisporic acid and its precursors.

Trisporic acid, okay.

And what's amazing is how it's made.

It involves collaborative metabolism.

Collaborative metabolism.

What does that mean?

It means neither the plus strain nor the strain can make the final hormone all by itself.

Each one has an incomplete biochemical pathway.

So they need each other.

Exactly.

They release intermediate chemicals into their surroundings.

And only the other strain has the enzymes to convert that intermediate into the next step or eventually into the active trisporic acid.

They swap precursors.

Wow, that's complex communication.

Isn't it?

And this chemical signal does two things.

It switches them from asexual spore production to sexual development, preparing them to mate.

And in some species like blakesley trispora,

this process massively ramps up the production of carotene.

Beta carotene, like in carrots.

It's the very same, which actually has commercial uses.

People harvest it.

So the mating process itself triggers pigment production.

Yeah, fascinating.

And those zygospores, you said they're tough.

Extremely tough.

Why so durable?

Well, their wall is packed with spore -pollinant.

Spore -pollinant.

Isn't that what's in pollen greens?

Makes them last for ages.

Exactly the same stuff.

It makes the zygospores incredibly resistant to decay, to harsh conditions.

They can sit dormant in the soil for ages, waiting for the right time.

Survival strategy.

Right.

Long -term survival.

And just to add another twist, sometimes you get zygospores.

Zygospores?

Like a zygote?

Kind of.

They're like zygospores, but they form without conjugation.

Sort of a virgin birth parthenogenesis, basically, from just one game tangium.

Huh.

Nature always has exceptions.

It certainly does.

Okay, so we've covered the basics, the mucoralis in some detail.

Should we explore some of the other, maybe more specialized, zygomycota?

Absolutely.

Let's talk about palobolus.

The name literally means hat -thrower.

Hat -thrower.

Okay, I'm intrigued.

This fungus grows on herbivore dung, cowpats, horse manure, that kind of thing.

Right.

Common habitat for fungi.

But it has this incredible problem to solve.

How to get its spores off the dung pile and onto fresh grass where an animal might eat them again.

Yeah, spores landing back on the dung isn't very helpful.

Exactly.

So palobolus evolved this amazing mechanism.

Its sporangio -4, the stoch, swells up with liquid, building enormous internal pressure, turgor pressure.

Like inflating a water balloon.

Sort of, yeah.

And then, when the pressure is high enough and often triggered by morning light, it explodes.

It explodes.

Violently.

It shoots the entire sporangium in the black hat at the top forwards, like a cannon.

How far?

It's astonishing.

Velocity is up to 27 meters per second.

It can launch the sporangium over 2 meters high and 2 .5 meters horizontally.

Whoa.

That's serious propulsion for a tiny fungus.

It really is.

Yeah.

The sticky sporangium lands on nearby grass and animal eats the grass.

The spores survive digestion?

Yep.

They pass through the gut unharmed and are deposited in a fresh pile of dung, ready to start the cycle over.

That is brilliant.

Nature's little artillery.

And there's a twist.

Palobolus sporangia can accidentally pick up passengers.

Passengers.

Larvae of parasitic nematodes, like Dictiocollis, the lung worm that affects sheep and cattle.

The fungus shoots the worm larvae onto the grass along with its spores.

So it helps spread animal parasites too.

Unexpected connection.

Yeah, an indirect vector.

Okay.

So from dung cannons,

let's look at the entomotherels.

The insect parasites, right?

Exactly.

Lots of species in this order specialize in attacking insects and other small critters.

How do they do it?

Various ways.

But one interesting thing is that some can actually live inside the insect host as wall -less protoplasts.

No cell wall.

Why?

It's thought to help them evade the host's immune system.

Harder to recognize and attack without that typical fungal wall.

Kind of stealthy.

Sneaky.

Any specific examples stand out?

Well, the life cycle of Basidiobolus ranarum is context doesn't even begin to cover it.

It's wild.

Basidiobolus ranarum.

Okay, lay it on me.

So it can shoot its spores.

It's knidia too.

But it's more like a mini rocket.

It has a special vesicle that contracts and squirts liquid backwards, propelling the spore forward.

Another projectile.

Yeah.

And these spores can land and germinate in different ways.

Sometimes they form capillicanidia.

Capillicanidia.

These have a sticky droplet at the tip, like an adhesive pad called a haptor.

This helps them stick on to things like mites crawling past.

Sticking to mites.

Where does that lead?

Well, the mite might get eaten by a beetle.

The beetle might then get eaten by a frog.

Inside the frog's gut, the fungus changes form again, becoming these gut stage cells.

Mite to beetle to frog.

That's quite a journey.

It is.

And perhaps surprisingly, Basidiobolus ranarum has also been linked to human infections.

Humans too.

Typically causes these subcutaneous swellings, usually in tropical areas, maybe from contaminated soil or insect bites.

It's a reminder that these life cycles can sometimes intersect with ours.

Definitely.

Okay, from parasites, let's talk about some helpers.

The glimals.

Ah, yes.

The unsung heroes of the plant world.

These fungi form one of the most widespread, ancient, and important mutualisms on Earth.

It's called Arbuscular Mycorrhiza.

AM for short.

Arbuscular Mycorrhiza.

I've heard of Mycorrhiza of fungus -fruit associations.

What's special about this type?

Well, Arbuscular refers to the structures they form inside the plant root cells.

These incredibly branched tree -like structures called Arbuscules.

Arbuscules.

Like little trees inside the cells.

Exactly.

And these are the main sites where the magic happens nutrient exchange.

Okay, what's being exchanged?

The fungus is brilliant at scavenging nutrients from the soil, especially phosphate, which plants often struggle to get.

It absorbs these minerals and transports them directly to the plant via the Arbuscules.

And what does the fungus get in return?

Sugar.

It gets photosynthates, the carbon compounds the plant makes using sunlight.

It's a classic trade.

Minerals for sugar.

A mutual partnership.

And you said ancient.

Incredibly ancient.

We have fossil evidence of Arbuscular Mycorrhiza dating back 460 million years.

Wow.

That's around the time plants were first colonizing land.

Exactly.

Many scientists believe this partnership was absolutely critical for plants to succeed on land in the first place.

The fungi basically acted as their root system extension, helping them get nutrients from poor, primitive soils.

So these fungi help make terrestrial life possible.

It looks that way.

They're fundamental.

These microscopic fungal networks extend way out from the plant roots, acting like this huge, super -efficient underground nutrient pipeline.

Improving plant growth, you said.

Massively.

Especially in poor soils.

Better growth, better water uptake, even increased resistance to diseases and stresses.

They're vital for healthy ecosystems everywhere.

So why don't they just live on their own if they're so good at getting nutrients?

Why need the plant?

That's the key.

They are obligate, mutualistic symbionts.

Obligate.

Meaning they have to have the plant.

Yes.

They cannot complete their life cycle without a plant host.

They've become completely dependent on the plant for their carbon, their energy.

Ah.

So the plant provides the essential energy source.

Right.

And it's not a trivial cost for the plant.

Supporting the fungus can use up maybe 20 % of the carbon the plant fixes through photosynthesis.

20%.

That's a lot.

It is.

But clearly the benefits in terms of mineral uptake, water, stress resistance, especially in tough environments, make it a worthwhile evolutionary bargain for the plant.

A cost -benefit trade -off that works.

Precisely.

And just to show the weird variations,

there's a related fungus, Geosophon pyreform, that isn't mycorrhizal.

Oh.

What does it do?

It forms a symbiosis not with a plant root, but with cyanobacteria blue -green algae.

It engulfs them.

Fungus and cyanobacteria.

Like a lichen almost.

Kind of resembles a lichen, yeah.

The fungus gets carbon and fix nitrogen from the cyanobacteria.

Another unique partnership within this lineage.

Amazing diversity.

Okay.

One last quick mention.

The Trachomycetes.

Ah, yes.

The hairy fungi.

These guys live in the guts of arthropods.

In the guts.

Like insects, millipedes.

Exactly.

Often commensally just living there without causing much harm, but sometimes parasitically.

How do they stay in place?

They have these specialized holdfast, unique anchoring structures to attach to the gut lining.

And they have their own weird spore types too, like trequospores, often with little appendages to help them spread.

Another whole weird world inside insects.

The fungal kingdom is full of them.

It really seems like it.

Okay, so we've taken quite a journey through the Zygomycota today.

We certainly have.

From their basic structure, that quinocytic mycelium, no swimming spores.

Right.

To their diverse reproduction of planospores, sporangia.

Those tough zygospores formed after that chemical chat.

The trisporic acid dance.

Yeah.

And the crazy dispersal methods, the passive wind and water, but also polobolus launching its hat.

Can't forget the hat thrower.

We looked at their roles.

Key decomposers, sometimes causing spoilage or disease.

Like rhizopus or mucormycosis.

But also useful in biotech, making food, making oils.

Two oleaginous ones, yeah.

Then the insect parasites, the entomophterals, but their complex lives.

And basediopolis.

And, hugely important, the glomales, forming those ancient, vital, arbustular mycorrhizae with plants.

Essential for land life, really.

So from unseen decomposers to planet -shaping partners.

Absolutely.

What really stands out for me is just the sheer adaptability,

the ingenuity of these organisms.

They're mostly hidden, working away unseen, but they are profoundly shaping our world.

Launching spores like rockets, building nutrient pipelines.

It's just incredible biological diversity.

A testament to life's creativity.

Definitely.

Which I guess leaves a thought for you, the listener, to mull over.

What other hidden microscopic worlds are out there, shaping our big macroscopic world in ways we're only just starting to glimpse?

Hmm, good question.

And how might studying these ancient relationships, these unseen connections, maybe inspire new solutions?

For agriculture, maybe medicine, or even just understanding our everyday lives better.

Lots to think about there.

We hope this deep dive into the zygomycota has given you a new appreciation for the amazing fungal kingdom.

Maybe a few surprising facts to share.

Hope so.

From all of us here at the Deep Dives, thank you for listening.