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From trumpets and spirals to floral arrangements, single cell organisms take on many strange and unique shapes. But they don't look like that just for fun, their shapes can help them with movement, hunting, and even defending themselves.

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SOURCES:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4368449/
https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002565
https://mmbr.asm.org/content/80/1/187
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4368449/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4460556/
https://jb.asm.org/content/182/5/1191
https://www.mdpi.com/2075-1729/10/12/355
https://www.cell.com/cell/fulltext/S0092-8674(05)00193-5
Thanks to Skillshare for supporting this episode of Journey to the Microcosmos.

The first 1,000 people to click the link in the description can get a free trial of Skillshare’s Premium Membership. Hi, hello.

It’s me again, Deboki, writer and occasional host for Journey to the Microcosmos. And I am here to confess something kind of shameful to you all: the first time I saw a picture of a tardigrade, I didn’t think it was real. I just remember looking at this animal that looked like a cross between a dog and the Michelin Man.

And it was even more strange to conceive of how tiny it is, and that out there in the world are just bits of moss with animals like this one gliding through them. Now that I’ve spent some more time in the microcosmos, tardigrades seem almost normal. Almost.

I mean, they are animals, and at the end of the day, you don’t have to be tiny to be a weird-looking animal. But animals have the advantage of many, many cells to build their different bodies. On the other hand, unicellular organisms like bacteria and protists, have less to work with.

And yet they manage to take on so many strange and unusual forms. Just think about it: if you were asked to draw a cell, what would you draw? Maybe your imagination is better than mine, but I would probably sketch out a vaguely round thing, maybe add some extra hairs on the outside if I’m feeling creative.

Nature has a lot more clever ideas though. Trumpets and spirals and floral arrangements, all made out of single cells. Of course, these shapes aren’t just for fun.

An organism’s shape is connected to the world it lives in, though sometimes the factors shaping them are beyond our understanding. It can be difficult at times to narrow down why a microbe takes on a particular shape when the reality of the microcosmos is that in any environment, you can find a whole plethora of shapes that might seem to have nothing in common. It’s also easy to look at the existence of a living thing and assume that every detail of its being has been optimized through eons of mutations and selection for a specific purpose.

And there is an extent to which that’s true. The world places all sorts of demands on life: the need for food, for reproduction, for warmth, for light, for dark, for movement. And we respond in kind by prioritizing and balancing those needs, and shape is one way we do that.

But it’s one thing to come up with stories for why something might be advantageous, It’s a much more involved process to prove it. Take spirochetes, for example, which are distinctive thanks to their helical shape. They’re also…not great for us.

They’re infectious, able to dig into us and invade our bodies. And it’s been hypothesized that part of how they do this is through that corkscrew shape, which might help them move through thick viscous solutions, you know, like our insides. But proving this hypothesis took a lot of work.

Scientists spent decades studying spirochetes in viscous solutions and mouse stomachs, as well as comparing them to other bacteria, all just to show that this shape gives them a physical advantage in colonizing bodies. And even then there are still so many aspects of the helical life and the advantages it provides them that are still conjecture. And that’s true for bacteria in general, which can take on so many shapes: spheres, rods, filaments, stalks.

But whatever the shape, the building material is the same: peptidoglycan, a combination of amino acid and sugar that links together to form a strong lattice that holds the bacteria and all its contents within. The structure of the bacterial cell wall can vary along with its shape. One group of bacteria, called gram-negative bacteria, generally have thinner walls and an additional outer membrane.

Gram-positive bacteria, in contrast, generally have a thicker, multi-layered wall. But like many categorizations in biology, this dichotomy is just a tad bit too simple. One of the largest groups of bacteria are cyanobacteria, and their diversity is even more astounding.

There are cyanobacteria like the Merismopedia, for example, that form flat colonies held together by a mucilaginous matrix like this, their round shape neatly arranged like candy dots. And then you have other cyanobacteria like these long filamentous forms that glide along surfaces. Cyanobacteria are generally categorized as gram-negative bacteria because their cells have that extra outer membrane we talked about.

But cyanobacteria also have a thick peptidoglycan layer, which makes them sort of like gram-positive bacteria too. And that strange combination of traits underlies the spectacular diversity of cyanobacteria. Single-celled eukaryotes, or protists, have a wide range of exteriors too.

But much of our understanding of their shape comes from their cytoskeleton, a network of filaments and microtubules that coordinates many essential functions in the cell. And when it comes to shape, it might seem unusual to focus on the amoeba, which is so often known for its shapelessness, especially as they move. It’s hard not to look at a blob and think of it as accidental, but the forming of pseudopodia--or false feet--to help the amoeba move, requires a complex architecture of microtubules to support this shifting shape.

And of course, there are many protists that take on very different shapes, whether that’s for defense or for food or for some other reason. There are pediastrum, that form these spiky colonies that protect them from algae eaters. And then there are the Opercularia, which look like little flowers attached to branches, and whose cilia you can see at work gathering food as it floats on by.

It’d be difficult to describe all the shapes that protists take on because there are just so many, even--it feels like--when compared to bacteria. Some scientists have argued that bacterial diversity is more internal than external, a function of metabolic reactions we can’t see. But protists have adapted more with their shape, leaving us with a world where the diversity itself is multifaceted.

We’ve spent this episode talking about the diversity of shapes in the microcosmos, in part because that’s what we can show you. But we’ve seen over and over again the way that shapes have misled scientists when it comes to classifying organisms, or the way that the shape of something can actually lead to more questions that can only be answered by studying the inside of the cell. But that’s the joy of shape: it’s an entry point into the microcosmos, a way for us to wonder about organism and environment alike.

Thank you for coming on this journey with us as we explore the unseen world that surrounds us. We’d like to also say thank you again to Skillshare for supporting this video. On Skillshare, you can put your new knowledge of shapes to good use with classes like “Vector Illustration: Design a Playful Character Using Geometric Shapes” which is taught by Illustrator Jonathan Ball.

From concept and sketch to creating vectors and shading, you’ll learn how to start with geometric shapes and ultimately end up with something from another dimension, or maybe even the microcosmos if you decide to create your own illustrated microbe. Skillshare is an online learning community that offers membership with meaning. With so much to explore, real world projects to create, and the support of fellow-creatives, Skillshare empowers you to accomplish real growth.

It’s curated specifically for learning, meaning there are no ads to distract you, and they’re always launching new premium classes, so you can stay focused and follow wherever your creativity takes you. And an annual subscription to Skillshare is less than $10 a month. If you’re one of the first 1,000 people to click the link in the description, you can get a free trial of Skillshare’s Premium Membership.

The names on the screen right now, those are our Patreon patrons, and without them this show would not get to exist. So, thank you to each and every one of you who support this channel. We’d like to let you know that we’ll be taking next week off from uploading, but we’ll have a brand new video for you on May 31st.

And if you’d like to see some very good microbes in the meantime, be sure to follow our Master of Microscopes James Weiss at Jam & Germs on Instagram. And you can also pre-order James’s book “The Hidden Beauty of the Microscopic World” wherever books are sold. And if you’d like to see more from us, make sure to click that subscribe button.