A Microscopic Tour of Death | Compilation

Summary

这段视频脚本深入探讨了微观世界中生物的死亡现象，揭示了即便是微小的微生物也遵循着食物、繁殖和死亡这些基本生命过程。视频中，通过不同的镜头展示了微生物死亡的多种方式，包括缓慢的、平静的、爆炸性的或令人毛骨悚然的过程。此外，视频还讨论了生命的定义，将其描述为一种化学系统，利用能量避免达到化学平衡。死亡则是维持远离平衡状态的系统停止存在的瞬间。视频通过展示各种微生物的死亡，包括被掠食者捕食、环境变化、甚至是科学实验中的紫外线照射导致的死亡，强调了生命和死亡的神秘性以及它们在生态系统中的重要作用。

Takeaways

• 🌿 **微观世界的生命循环**：微观生物尽管形态奇特，但它们的生活依然围绕着食物、繁殖和死亡这些基本要素展开。
• 🔬 **技术升级**：得益于观众的支持，频道多次升级显微镜，使得观察到的微观世界更为清晰。
• 🐌 **死亡的多样性**：微观生物的死亡形式多样，有的平静缓慢，有的则突然或令人毛骨悚然。
• 🧬 **生命与死亡的化学本质**：生命是一个使用能量来避免化学平衡的化学系统，而死亡是维持远离平衡状态的系统停止存在的瞬间。
• 🌱 **环境因素对生命的影响**：温度、氧气浓度、pH值和水质等环境因素的变化都可能导致单细胞生物死亡。
• 🕸️ **捕食者与猎物的关系**：即使是强大的捕食者，如Loxophyllum meleagris，也可能成为其他物种的猎物。
• 🦠 **微生物的相互作用**：通过观察微生物的死亡，我们可以了解到它们是如何与环境互动，以及它们自身是如何运作的。
• 🌐 **死亡的普遍性**：无论是个体细胞、生物体还是整个物种，死亡都是生命循环的一部分。
• 🍄 **真菌与线虫的致命关系**：某些真菌，如Arthrobotrys，能够在氮稀缺时转变为捕食者，捕捉并消化线虫。
• 🔦 **光的双刃剑**：紫外线光虽然能够帮助科学家观察微生物，但长时间曝光也会导致微生物死亡，展示了光的有害一面。
• 🌟 **光毒性**：紫外线可以激发细胞内的化学物质，产生荧光，但同时也可能生成有害的活性氧，导致细胞破裂和死亡。

Q & A

微生物世界中的生命基本要素有哪些？

微生物世界中的生命基本要素包括食物、繁殖和死亡。

为什么说微生物可能'发明'了死亡？

这可能是因为微生物作为生命形式的早期存在，经历了生命过程中的死亡，从而可以比喻性地说它们'发明'了死亡。

视频中提到的微生物死亡有哪些不同的方式？

微生物的死亡方式包括缓慢的、平静的死亡，爆炸性的或令人毛骨悚然的死亡。

视频中提到的显微镜升级对观察微生物死亡有什么帮助？

显微镜的升级使得观察者能够更清晰地看到微生物的死亡过程，包括它们的细胞结构和死亡时的行为。

视频中提到的Lacrymaria olor是如何捕食Loxophyllum meleagris的？

Lacrymaria olor利用其泪滴形状的身体和颈部的延伸，可以伸长至其身体长度的八倍来寻找猎物。它能捕捉并吃下Loxophyllum meleagris，尽管后者体型较大。

为什么说单细胞生物的死亡原因多种多样？

单细胞生物可能因为温度变化、氧气浓度、pH值、水质等多种环境因素而死亡。

视频中提到的Paradileptus的死亡过程是怎样的？

Paradileptus在游动数小时后停止运动，其形状开始变化，最终溶解消失，似乎不仅杀死了自身，还影响了附近的一个小型绿色细胞。

视频中如何描述微生物死亡时细胞膜的变化？

在某些微生物死亡时，细胞膜会经历溶解（lysis）的过程，释放其内部物质到周围环境中。

视频中提到的关于生命的定义是什么？

生命被描述为一种化学系统，它利用能量来防止自身达到化学平衡状态。

视频中提到的关于死亡的定义是什么？

死亡被定义为维持远离平衡状态的系统停止存在的瞬间。

视频中提到的紫外线对微生物有什么影响？

紫外线可以导致微生物的光毒性反应，引起细胞膨胀并最终破裂，导致死亡。

视频中提到的Blepharisma因为什么化学物质而死亡？

Blepharisma因为其体内的红色色素分子blepharismin在紫外线和氧气环境下形成活性氧，导致细胞死亡。

Outlines

00:00

🌐 微观世界中的生命循环

本段介绍了微观世界生物虽然形态各异，但它们的生活依然遵循着与我们相同的基本规律：食物、繁殖和死亡。微生物虽然顽强，但它们也会死亡，甚至可以说它们“发明”了死亡。视频中展示了不同形式的微生物死亡过程，有的缓慢而平静，有的则是爆炸性或令人毛骨悚然的。此外，还提到了节目使用的显微镜技术随着观众支持而升级，使得我们能够更清晰地观察到这些生命现象。

05:03

🦠 微生物的死亡因素

这段内容探讨了导致单细胞生物死亡的多种因素，包括捕食者、温度变化、氧气浓度、pH值、水质等。描述了单细胞生物因渗透压导致细胞破裂的情况，以及一些死亡原因不明的案例，比如 Paradileptus 在游动数小时后停止活动并开始变化直至消失。此外，还讨论了微生物与环境的相互作用、它们自身生理机能的工作方式，以及它们之间的联系。

10:08

🔍 生命与死亡的化学定义

本段深入探讨了生命和死亡的化学定义。生命被描述为一种化学系统，它利用能量来防止自身达到化学平衡。而死亡则是维持远离平衡状态的系统停止存在的时刻。文中还提到，虽然我们每天都会经历细胞的死亡，如皮肤细胞的脱落，但整个生物体的死亡只有一次。此外，还提出了生命体在不同尺度上的死亡，包括个体细胞的死亡、个体生物的死亡以及物种的灭绝。

15:09

🕸️ 真菌与线虫的致命关系

这一部分讲述了一种名为 Arthrobotrys 的真菌如何从分解者转变为捕食者，并通过陷阱捕获并消化线虫。描述了真菌如何利用菌丝形成环状陷阱，并通过模仿线虫的费洛蒙或食物气味来吸引线虫。当线虫穿过这些环时，环会收缩并捕获线虫，随后真菌的菌丝会穿透并瘫痪线虫，并从内部消化它。文中还提到了其他能够捕获线虫的真菌，以及它们在生态系统中的重要作用。

20:12

💥 微生物的光毒性死亡

本段描述了紫外线（UV）光如何导致微生物的死亡。紫外线可以激发细胞内的化学物质，产生荧光并形成活性氧，这些活性氧会损害细胞内的分子并干扰生命所需的化学反应。展示了几种微生物在 UV 光照射下迅速死亡的情况，说明了即使是对生存至关重要的光，也必须谨慎处理，因为它也可能是致命的。

25:17

🌟 光与微生物的复杂关系

这段内容讨论了光对微生物的影响，以及科学家如何通过调节光的波长、强度和持续时间来控制光毒性反应。特别指出了 UV 光下 blepharismin 色素分子对 blepharisma 的防御作用，以及在适当的光照条件下，微生物可以生存而不受伤害。最后，强调了虽然我们可能认为微观世界与我们不同，但我们如何照亮这个微观世界，不仅影响我们观察生物的方式，也塑造了它们的生活。

Keywords

💡微生物

微生物是一类个体微小、结构简单的生物群体，包括细菌、病毒、真菌以及一些小型的原生动物等。在视频中，微生物是探索微观世界死亡现象的主要对象，它们的生存和死亡揭示了生命与环境之间的复杂联系。例如，视频中提到了通过显微镜观察到的微生物死亡的各种形式，如原生动物的裂解、水熊虫的死亡等。

💡死亡

死亡是生物体生命活动终止的状态，是视频中探讨的核心主题。视频中通过展示不同微生物的死亡过程，引发对生命、死亡和自然循环的深入思考。例如，文中描述了原生动物在捕食者攻击下、环境变化中或因内部机制故障导致的死亡。

💡捕食者与猎物

捕食者与猎物的关系是自然界中普遍存在的一种生物相互关系，视频中通过展示微生物世界中的捕食行为，如洛索菲勒姆（Loxophyllum）捕食轮虫，以及它们自身也可能成为其他生物的食物，揭示了食物链中捕食者与猎物之间的复杂动态。

💡环境因素

环境因素指的是影响生物生存的各种外部条件，包括温度、氧气浓度、pH值和水质等。视频中提到，环境因素的变化是导致微生物死亡的重要原因之一，如温度变化导致的渗透压问题，或是氧气浓度的不适宜导致细胞无法进行正常的呼吸作用。

💡细胞裂解

细胞裂解是指细胞膜破裂，导致细胞内容物释放到外界环境中的过程。在视频中，细胞裂解是微生物死亡的一种形式，如原生动物在捕食压力下或因内部机制故障导致的裂解，这显示了生命体在面对极端情况时的脆弱性。

💡光毒性

光毒性是指生物体因暴露在光线（尤其是紫外线）下而产生的毒性反应，可能导致细胞损伤或死亡。视频中通过紫外线照射实验展示了光毒性的效果，如原生动物在紫外线照射下迅速死亡，说明了科学研究中对光的使用需要谨慎，以免对研究对象造成伤害。

💡荧光显微镜

荧光显微镜是一种利用特定波长的光激发样本发出荧光的显微镜，常用于观察细胞或组织的特定结构。视频中提到了荧光显微镜的升级，使得观察者能够看到微生物在紫外线照射下的荧光反应，这有助于研究者区分不同的微生物群体。

💡活性氧

活性氧是一类具有高度反应性的氧化合物，它们在细胞代谢过程中产生，并在光毒性反应中起到关键作用。视频中解释了活性氧如何在紫外线照射下形成，并可能导致细胞结构的损伤，从而引发细胞死亡。

💡渗透压

渗透压是指两种不同浓度溶液之间的压力差，它会导致水分从低浓度溶液向高浓度溶液移动。视频中提到，当单细胞生物的渗透压调节机制失效时，细胞可能会因为水分过多而破裂，这是微生物死亡的一种方式。

💡紫外线

紫外线是电磁谱中波长较短的光波，具有一定的杀菌作用。在视频中，紫外线被用于荧光显微镜中以观察微生物，但同时也展示了它对微生物的致命影响，即通过产生光毒性导致细胞损伤和死亡。

💡原生动物

原生动物是一类单细胞或简单多细胞的生物，它们在生态系统中扮演着重要的角色。视频中多次提到原生动物，如轮虫被纤毛虫捕食，以及它们在环境压力下的死亡，展示了原生动物在微观世界中的生存挑战。

Highlights

微生物虽然奇特，但它们的生活仍然围绕着与我们相同的基本要素：食物、繁殖和死亡。

即使微生物非常顽强，它们也会经历死亡，甚至可以说它们“发明”了死亡。

通过显微镜，我们观察到微生物死亡的多种形式，包括缓慢、平静的死亡，以及爆炸性或令人毛骨悚然的死亡。

微生物的死亡揭示了它们与环境的相互作用方式、它们自身身体的工作原理，以及它们之间的联系。

通过观察微生物的死亡，我们了解到生命的化学系统是如何利用能量来避免达到化学平衡的。

死亡是维持远离平衡状态的系统停止存在的时刻，可以发生在生物体的单个部分、单个细胞或整个有机体上。

微生物的死亡方式多种多样，包括被捕食者捕食、环境因素导致的死亡，以及细胞内部机制失效导致的死亡。

通过显微镜升级，我们能够更清晰地观察到微生物的死亡过程，这得益于观众的支持。

微生物的死亡不仅仅是一个自然过程，它还揭示了生命如何与环境相互作用，以及生命体内的化学物质是如何工作的。

微生物的死亡过程可以帮助我们理解生命的化学本质，以及生命是如何避免达到化学平衡的。

微生物的死亡揭示了生命的脆弱性和复杂性，以及生命如何在我们的显微镜下展现出它的多样性。

微生物的死亡过程提供了对生命本质的深刻见解，以及生命是如何在不断变化的环境中生存和繁衍的。

微生物的死亡是自然秩序的一部分，它揭示了生命如何通过捕食和被捕食来维持生态平衡。

微生物的死亡过程揭示了生命的化学系统是如何利用能量来避免达到化学平衡的，这是生命的基本特征。

微生物的死亡过程展示了生命如何在面对环境压力时展现出其适应性和生存策略。

微生物的死亡揭示了生命如何在不断变化的环境中生存和繁衍，以及生命是如何在面对捕食者时展现出其生存策略的。

微生物的死亡过程提供了对生命本质的深刻见解，以及生命是如何在不断变化的环境中生存和繁衍的。

Transcripts

As strange as the creatures of the microcosmos are,

their lives still revolve around the same fundamentals that ours do.

There’s food, there's reproduction, and there's death.

Yes, even microbes, hardy as they can be, experience death.

In some ways, you could say they invented it.

And on our journey through the microcosmos, we’ve watched those deaths through many lenses.

Some are slow, calm affairs, while others are explosive or creepy.

And today, we’re going to try something new for our channel.

We have gathered a few of our favorite episodes about death in the microcosmos so that we

can see where our journey has taken us.

So yeah, this is the kind of video you can turn on, and leave on for awhile.

This first video is also one of our oldest, so you’ll notice that a lot of

footage in it looks very different from what we show these days because thanks to the support

of our viewers, we’ve been able to upgrade our microscope

multiple times over the course of this show.

So the microscope may be different.

But the death, well, the death remains the same.

This round little unicellular creature came to us via a plankton net, a mesh with tiny,

microscopic holes through which we ran hundreds and hundreds of liters of water, letting us

collect anything too large to pass through.

We haven’t been able to identify this species yet, making it a bit of a mystery.

But the bigger mystery is still to come because this little creature is about to undergo that

most universal and unknowable experience of all, death.

Death comes to the microcosmos in many forms.

Like this Stentor Polymorphous, slowly expelling the contents of its once trumpet-like body

into the surrounding environment.

Or this dead larva, whose exoskeleton is now an inanimate host to two unicellular organisms.

Even the mighty tardigrade, which has survived as a species through multiple mass extinctions,

is not immune to death.

This is, of course, the natural order of things.

Predators hunt, and their prey attempts to survive, with varying levels of success.

This is Loxophyllum meleagris, a large unicellular organism that we’ve shown before eating a rotifer.

This one is practically stuffed with those multicellular creatures, we counted five rotifers inside of it.

But sometimes the predator becomes the prey, and even the Loxophyllum meleagris has to

find ways to ensure its survival when other species come after it.

This seemingly unlikely threat is the Lacrymaria olor.

Its name in Latin means “tears of a swan”, a name that suits both its teardrop shape

and its neck-like extension, which gets up to eight times longer than its body in search of prey.

Sometimes, we can see its neck poking out of the dirt on our microscope slide.

But even knowing that, you’d be forgiven for thinking it unlikely that something so

small could pose a problem for those larger Loxophyllum.

And yet, the Lacrymaria manages to take quite a chunk out of the Loxophyllum.

The Loxophyllum though, survives thanks to its ability to regenerate the piece that was taken,

but not all prey gets so lucky.

Here, this rotifer has been killed by a heliozoan, destined to become food, a fate that this

flagellate is about to share as it becomes captured by a heliozoan that is in the middle

of cell division.

The flagellate has been trapped by those long extensions, called axopods, that radiate out

from the heliozoan’s body.

As the flagellate comes further in, it will be engulfed by the cells into its own food

compartment called a vacuole.

There, it will be lysed open and its contents digested by the heliozoa.

In the end though, the natural order comes for predators too.

Here, another heliozoan’s dying cellular body attracts the various

decomposers of the microbial world.

Aside from predators, there are many other factors that lead a single-celled organism

to die, changes in temperature, oxygen concentration, pH, water quality, so much more.

This single-celled organism is swollen because the water surrounding it is entering the cell

via osmosis.

Many organisms have water pumps called contractile vacuoles that they use to push water back

out and prevent that swelling.

But as in the case of this organism, sometimes those contractile vacuoles stop working,

and when that happens, the cell swells and explodes.

Other times, the cause of death is harder to determine, like this Paradileptus that

spent several hours swimming before going still, its shape beginning to change until

it melts away, seeming to kill not only the Paradileptus but this small green cell swimming

nearby, but leaving other smaller flagellates seemingly unaffected.

And this brings us back to the beginning, with our mystery organism that is about to

undergo a death laden with more mysteries.

At first, the cell looks like it’s just melting away, dissolving into something that

resembles a microbial Milky Way, except that for a few seconds, it almost looks like the

cell membrane is able to close itself back up.

We think, though we can’t know for sure, that some of the mechanisms inside the cell

are still working, and that the organism is trying to recover.

But alas, survival is not in the cards.

Its membrane goes through lysis, releasing its insides into the surrounding environment.

This death is unlike any other kind of death we’ve observed under our microscope, and

we’re still not sure what caused it.

Perhaps there were so many organisms in the sample that they depleted the oxygen, and

this organism could not continue cellular respiration.

But perhaps it was something else.

Death at every size holds its own mysteries, but it also reveals.

The observations we make, even the guesses we come up with, tell us about the way these

microbes interact with their environment, the way their own bodies work, and the connections

that exist between them.

It is only ever in the mysteries that knowledge is waiting to be found.

So we just saw a small fraction of how many ways there are for microbes to die.

But maybe now you’re asking yourself a more fundamental question: what even is death?

Well, weirdly, none of us will ever fully know the answer.

But that doesn’t mean we can’t try to use what we know of chemistry and life to

begin to describe it, as we’ll see in our next video.

This is a ciliate, Loxodes magnus.

It is about to die.

Of course, depending on your time scale, we’re all about to die.

To the grand canyon, or the sun, things that have existed for millions or billions of years,

we are each weird little bubbles of peculiar chemistry that form and then pop,

form, and then pop.

But this ciliate, and with our new microscope you can really see those cilia beating, is

about to pop right before your eyes.

It looks fine right now.

You can even see, inside it, it’s last meal, a Trachelomonas.

So we don’t think it’s starving to death.

It seems to be trucking along just fine.

Loxodes Magnus are microaerophilic organisms, preferring a low concentration of dissolved

oxygen in their environment, but not too low.

So maybe the concentration on the slide was too high, though we’ve witnessed many others

who have been just fine in our preparations.

So no, we can’t tell you why this ciliate is about to die, but we can tell you that

right here, that’s where James, our master of microscopes, first saw something strange.

The moment the ciliate shifted direction, a little trail of cell membrane and cytoplasm.

No reason.

Nothing grabbed it, it didn’t snag on anything.

But a little bit of what was once a part of the organism was suddenly, no longer a part of it.

That cytoplasm is full of complicated molecules that are what chemists would call, far from equilibrium.

Equilibrium is the situation in which chemicals no longer have a tendency to react over time.

In general, a thing that you can say for sure is that all the stuff outside of living cells

is either at chemical equilibrium, or it is headed there.

Whereas stuff inside cells is not at equilibrium, and it’s not headed there either.

How are all of these chemicals that, if left alone, would rapidly reach equilibrium managing

to not do that?

Life.

That is what life is.

A bunch of chemicals that take in energy in order to keep each other from reaching equilibrium.

Quick break from our friend, the way we define life in biology classes is, wrong.

It’s not even really a definition, it’s a set of qualifying factors.

Life has to take in energy.

Life has to reproduce, it must respond to its environment, it must consist of cells.

This is not a definition, it’s an attempt to draw a line, to create a boundary.

And that makes sense for things that are actually amorphous and complicated, like social constructs.

But life is not a construct of our opinions, but of reality.

Life is a chemical system that uses energy to keep itself from reaching chemical equilibrium.

Why do they do it?

Oh, well maybe let’s not go that deep, at least not today.

Suffice it to say, a system that did this developed on this planet and now, billions

of years later, it is still doing it.

We have many things in common with this ciliate, and not to belabor the point, but one of those

things is that we will die.

You’ve may have noticed by now that this video isn’t about what life is, it’s about

what death is.

It’s just that, first, we had to define life.

Life is chemicals working together to take in energy to keep themselves far from equilibrium.

Death is not the return to chemical equilibrium.

The process of decay can last decades.

Likewise, many parts of my body will return to equilibrium over the course of my life,

I’m shedding skin cells right now and so are you.

The atoms and molecules of my body are replaced with new ones over and over and over again.

But I will only die once.

Likewise, our ciliate has been shedding cytoplasm and cell membrane for minutes now, and that

shed cytoplasm is dead, no doubt.

But the organism lives.

Its chemistry continues.

For now.

Death is the moment when the system that maintains the far from equilibrium state ceases existence.

And we can imagine that at many scales.

That can happen to individual bits of an organism, as it is happening to the chemicals spilling

out of our Loxodes right now.

It can also happen to an individual cell in an organism.

And that happens all the time.

It is happening right now inside you.

It can also happen to an organism.

That’s what we usually think of as death, with our focus, so often, on the individual.

But we can keep moving up the scale and find yet other kinds of death.

When a common genetic system that was useful for keeping many similar but individual organisms

alive ceases to exist, that is an extinction.

A kind of death.

And when the system that has kept all life on earth far from equilibrium for billions

of years, that system that we all share of nucleic and amino acids, when that ceases

to exist, that will be something else.

A terrible kind of death that we do not even have a name for.

But it will be a death.

The largest death, I suppose, until heat death, when everything in the universe has found equilibrium.

Our ciliate is about out of time now.

I don’t know when we can call it, when we can pronounce the time of death, but this

seems as good a time as any.

Here, we have death.

The system that was using energy to keep itself from reaching equilibrium has ceased to exist.

Hey, welcome back. If you’ve come out of that video with some

existential dread about the state of the universe, that is very reasonable.

However, on our next stop in this journey, we’re going to argue that sure, chemical

equilibria are scary, but if you’re a nematode, maybe you should worry about fungi first.

There are plenty of horror stories that begin innocuously enough.

A new home, a camping trip with friends, a doll purchased at an estate sale….

This one starts with some ponds, the same set of ponds that James, our master of microscopes,

has been sampling every week for the past three years.

Which means that he’s collected so many microbes from these waters that you might

think they’d get a bit boring or redundant.

But you should never underestimate nature’s capacity for surprise.

Recently, James came home with some samples from these ponds.

And as usual, he prepared some slides and checked on the organisms within, finding some

nematodes like this one slithering about on the slide.

And all seemed well, so he stored the slides and his new friends in a humidity chamber

and waited to observe them after a few more days.

But two days later, all would not be well.

This is where we build our suspense.

In a movie, this would be the moment where we assess the unsettling basement or the dark

woods, and then consider retreating to safety.

This is the creepy doll, only there hasn’t been any thumps in the middle of the night,

so everything seems okay, right?

We’re looking at the spores of a fungus, one belonging to the group Arthrobotrys.

And when it’s just floating around like this, it seems quite harmless—especially

when compared to the nematodes we showed earlier, which are part of a whole family of worms

that are notorious for their parasitic lifestyle.

And if you were to write off Arthrobotrys as a potential threat, you would be correct…

most of the time.

It does spend much of its life aligned with the dead, but only to sustain itself on the

remains of decayed life and organic matter.

Arthrobotrys species are found all around the world, occupying everything from soil

to animal feces in the many varied climates that make up our planet.

And wherever it is, the fungus ensures that nutrients like nitrogen from dead organisms

and other waste cycle through ecosystems.

But when nitrogen is scarce, these fungi will resort to hunting it down from living sources.

And what better prey than the nematode, a fellow dweller of the soil and one of the

most abundant animals on earth?

When James put his slides into the humidity chamber, he had no notion of what these nematodes

would be facing, and so no expectation of what he would find.

But when the slides came back out, what he observed was something he’d only seen once

before, in a drawing done two years ago by one of his close friends, Katelyn Solbakk.

In it, you can see a nematode whose body has been clinched

into segments by some kind of bulbous, thing.

What you’re seeing is the fungus’ most brutal design.

But to get there, it must morph from decomposer to predator, no longer consuming what has

already been dead, but actively killing.

It begins by weaving a trap out of itself.

It threads the hyphae of its mycelium out and then back in, forming a living loop that

repeats to form a net.

But a net is only one part of a trap, the other part is the lure.

The fungi can find nematodes by following traces of their pheromones like they’re

breadcrumbs.

And more nefariously, they can mimic the smell of certain food cues to draw the worm in,

like a siren working through scent instead of song.

The nematode has no reason to suspect anything, even as it swims closer and closer and eventually

through the fungal rings.

But as it does, the movement of worm and water triggers the rings to constrict.

The worm is trapped, but the worst is still yet to come.

The fungus’ hyphae begin to grow off from the loop, puncturing the worm’s cuticle and paralyzing it.

The threads swell up into a bulb that produces more hyphae to spread through the rest of the nematode.

And then the fungus feeds and feeds, quickly digesting the rest of the nematode’s body

from within.

It is a gruesome death.

Here is one nematode, just recently trapped.

And here is the worm again, four days later.

You can see the infection bulb where the fungus first punctured and expanded.

And the whole body of the worm seems taken over, no longer a clear tube, but instead

a corpse that has become home to its cause of death.

The Arthrobotrys fungi are not the only ones capable of trapping and feeding upon nematodes.

There is a whole range of nematode-trapping fungi with their own methods, though the species

Arthrobotrys oligospora is perhaps the most plentiful of these fungi and also the best studied.

Maybe it’s just us, but it’s somewhat unsettling to realize that this insidiousness

is all the work of a fungus, a thing that can seem so inert compared to the wiggling,

active worm that it targets.

But fungi do have a kinship with horror stories.

Their frequent role as decomposers naturally connects them with the dead.

Plus, they come equipped with their own creeping sense of dread with images of mycelia weaving through bodies.

And authors have drawn inspiration from the notion of fungal horror.

There are many works--like the famous Gothic tale We Have Always Lived in the Castle, or

the short story “The Voice in the Night,” or recent novels like Mexican Gothic and Wanderers—

that draw on everything from poisonous mushrooms to colonizing fungi to create their terror.

But whatever we seek to scare ourselves with in fiction, horror has its purpose in nature.

As we’ve pointed out, nematodes are one of the most abundant animals on earth.

They play an important role in decomposition...but they’re also the source of many diseases—both

in animal bodies and in plants.

So having them be slightly less abundant is important to our ecosystem as well.

In fact, scientists have been studying these fungi to develop better nematode-fighting

strategies for agriculture.

So as is the case with many good horror villains, there is a version of this story where the

nematode-trapping fungus is the hero.

Unless, of course, you’re the nematode.

And for our last video, our microbes are dying at the hands of an unusual enemy.

It’s James, with an UV laser, in the laboratory.

Maybe it sounds like a microscopic version of the game Clue, but there’s a point to it all,

we swear.

Blepharisma have appeared on our channel several times before.

In fact, this channel got its start thanks to a video that James, our master of microscopes,

once posted of a Blepharisma dying.

Around three million people watched that video, including me, your host Hank Green.

So if you enjoy this channel, you can thank that dead Blepharisma.

But perhaps you should wait for another day to thank them.

Because in about ten seconds, you’re going to watch a Blepharisma explode.

Here it is, glowing with autofluorescence underneath UV light.

You can see its oblong shape and oral groove outlined in red…but not for long.

The red becomes brighter and brighter, but it also looks like it’s starting to expand.

And then suddenly, the walls of the blepharisma burst, the organism popping like a crimson balloon.

The blepharisma bubbles and pours into its surroundings

and it all happens within a matter of seconds.

Let’s watch it again.

Dead or dying microbes are a common enough sight in our journey through the microcosmos.

And there are many potential culprits behind these deaths: predators, accidents, environmental

changes, the inevitable march of life into death.

But the culprit this time… well, it was us.

Us and the UV light that is part of our new fluorescence microscope upgrade.

And our UV light has been very exciting for us.

In particular, it’s allowed us to look for methanogens, or Archaea, which sometimes take

up residence inside protists.

Under normal light, it’s hard to tell the tiny archaea and the tiny bacteria apart.

But under UV light, the archaea will shine blue.

So UV can reveal new aspects of the microcosmos.

But if you’ve ever fallen asleep on a beach or just stayed out in the sun a bit too long,

you may have also experienced the darker side of UV light.

No one wants a sunburn, but fortunately, we have defenses, like hair, and melanin, and

sunscreen which can block or absorb UV rays before they cause further damage in our cells.

We also, and this is crucial, have more than one cell...so if some of them die, which when

you get a sunburn they do, the rest of our bodies can live on.

Not all organisms have these sorts of protections.

Or if they do, they’re designed for exposure to the sun, not the intense scrutiny of our UV light.

So when James wants to hunt Archaea, he has to be careful.

He can quickly shine the UV light to see if anything blue appears.

But he has to quickly shut it off.

Because as we’ve seen, even a few seconds of exposure to the UV light will kill off

his pond buddies.

We want to note that as we said earlier, death is a common reality of the microcosmos…we

just usually prefer to walk in on a microbe dying rather than being the cause of death.

But for this episode, we decided to make an exception and use our UV light for an extended

period of time, with the knowledge that it would kill the microbe we were watching.

Because these explosions illustrate the cost of doing business with light.

The word for this business is phototoxicity.

Death by light.

And while it can happen under other monochromatic lights, the particular wavelength and intensity

of our UV light makes it much more harmful to our organisms than our other red, blue,

or green light sources.

This death starts with excitation.

When the light hits the organism, it can potentially excite chemical structures inside the cell,

sending electrons up and down, and producing fluorescent colors in the process.

But the colors aren’t the only thing that gets created.

If there’s oxygen around, it will react with the excited fluorescent molecule, creating

what are known as reactive oxygen species.

In biology, reactive oxygen species are byproducts of different cellular processes that metabolize

oxygen, which can make them part of normal life.

There are even reactive oxygen species that are involved in signaling pathways.

But the “reactive” in their name is key to what makes an excess amount of them dangerous.

If you are an organism, and you are, there are a lot of reactions you want to have happen

in your cells.

You want your DNA to link together correctly, you want your enzymes to find the right substrates.

But reactive oxygen species are happy to react with all of those molecules too, damaging

them and getting in the way of the chemistry that we need to survive.

What phototoxicity will look like depends on the organism and the light being directed at it.

For the organisms we’ve been showing here, like this homalozoon, the overall effect of

this intense UV light seems to be unanimous: the cell swells up and bursts open, like a

galaxy erupting on our slide.

But while the overall effect is the same, the internal machinations are likely different,

triggered by a complex interplay of different chemicals that nonetheless react to our light

source in a similar, catastrophic fashion.

While we’re not sure of the culprits behind the homalozoon’s death, we can identify

one of the chemicals that likely sets off the blepharisma’s death.

It’s the reddish pigment molecule called blepharismin that gives the ciliate its color

under more normal circumstances.

Outside of the UV light, you can see the membrane-bound pigments neatly distributed along the rows

that stretch from one end of the blepharisma to the other.

But under our UV light and with oxygen in the environment, the blepharismin reacts to

form reactive oxygen species, and death follows quickly from there.

But while toxic in our experiment, we should note that the blepharismin serves a key purpose

for the blepharisma: defense.

These pigment molecules are toxic to some of Blepharisma’s predators in both the light

and the dark.

That makes the pigment somewhat like UV light: necessary for survival, yet also a delicate negotiation.

But in the same way that we manage our relationship with the sun, scientists have learned ways

to manage these phototoxic reactions.

They’ve had to in order to understand how we can use fluorescence microscopy to study

cells and organisms.

They’ve learned how to modulate wavelength and intensity and duration, along with many

other factors, to wield light in a way that better serves their purposes.

In the case of the blepharisma, for example, scientists found that using a moderate light

for around 1 hour wasn’t much of a problem for them.

But with more time under the light, the cells would eventually die.

It’s easy to think of the microcosmos as a separate world from us, even when we know

that the microscope is a bridge between large and small.

But these deaths at the hand of our supposed bridge are a cautionary sign that we are encountering

microbes in a world that is both natural and manufactured at the same time.

The way that we light that world impacts the way we see the organisms, and it also shapes

their lives—reminding us that they are stronger often than we can fathom, but fragile nonetheless.

And that brings us to the end of our tour of death in the microcosmos today,

an end to a story of ends, you might say.

But maybe what we’ve seen today is that there really is no end, is there?

Just pauses on individual stories that nonetheless endure in the remains of the world left behind.

Thank you for coming on this journey with us as we explore the unseen world that surrounds us.

And thank you to all of our patrons who make videos like the ones we’ve watched today possible.

This channel could not exist without your support and we are so thankful for it.

If you’d like to join the list of patrons you’re currently seeing on your screen,

you can go to patreon.com/journeytomicro.

And if you’d like to see more from our Master of Microscopes, James, you can check

out Jam & Germs on Instagram, and if you’d like to see more from us, there’s probably

a subscribe button somewhere nearby.