In 1703, an anonymous Englishman, known to history only as Mr. C, wrote to the Royal Society of London to report on a peculiar
observation he’d made using only a simple microscope. He’d been looking at the roots of pond-weed,
but as he looked closer, he found attached to the roots, “‘many pretty branches, compos’d of rectangular oblongs and exact squares.’” At first, he assumed these geometric attachments must be salt crystals. But the more he experimented and looked through
his microscope, the more he realized there might be something amazing going on here. These tiny, beautiful shapes seemed kind of plant-like. Today, with the benefit of many, many more observations, and far superior equipment, we know that this 18th century letter is one of the earliest descriptions
of a diatom, a photosynthetic, unicellular algae that can become so plentiful that oceanic
blooms of these organisms, which we cannot see individually without a microscope, are
nonetheless visible from space. But, we wouldn’t be talking about diatoms
if we needed to be in space to observe them. You can find these tiny organisms just about
anywhere that has water and light. Looking at them through a microscope, you
might understand why microbe hunters are so fond of them. They have been called “the jewels of the
sea”. Those beautiful outer shells are called frustules,
and they set diatoms apart from every other living creature. Unlike the organic cell walls and membranes
we associate with most cells, frustules are made out of inorganic silica, enclosing the cytoplasm of the diatom in, what is basically, glass. Silica shells take less energy to make and
maintain compared to their organic counterparts, but they do come with a trade-off. Glass is…well, it’s glass. It’s hard to expand if you’re a unicellular
organism trying to undergo asexual mitosis when your cell is inclosed in a rigid, inorganic material. Instead, when diatoms divide, the daughter
cells take the old frustule and divide it between them, which means that the daughter
cells are both going to be smaller than their parent, and they’re never going to grow
any bigger. And as diatoms keep dividing, the daughter
cells keep getting smaller and smaller. If this goes on forever, the diatom will get
so small that it cannot survive. But diatoms that are starting to get too small
can avoid that fate through sexual reproduction, which is kind of a refresh button that lets
them construct a new frustule for a larger daughter cell. For the most part, diatoms can’t actually
move—they just go wherever the water takes them. But some diatoms are able to glide along a surface using a slit in their frustule called a raphe. This allows them to secrete
mucus that sticks to a surface but, how does that mucus help them move? We...don’t know. We can see that they move, so they must be able to And we can see that mucus is always left behind when they do it, but we don't know the exact mechanism of how it works. You and I, of course, move using muscles. And the moluecules responsible for that in us are actin and myosin. Here’s a wild thing, in 1999 some scientists put actin disrupting compounds in solution with diatoms and those diatoms lost their ability to move. So while diatom motility remains something
of a mystery, these tiny, jewel-encrusted algae move using the same molecular systems as us. If you've been looking closely, you might be wondering what these bubbles are, and if you are we hope we can surprise
you. Those are oil droplets, and they store energy for the diatom when they might be having trouble finding light or their usual nutrients. These little organisms are so good at creating
this fatty oil that scientists have wondered whether we might use diatoms as tiny factories
that turn sunlight and carbondioxide into fuel not just for them, but for our future
airplanes. It might be tempting to think of these cells just as little microscopic jewels, just something nice to look at, but they also have a huge impact on our world. Of all of the photosynthesis being done on Earth, around 1/5 is done by diatoms, which puts them on par with all rainforests on earth combined. and it means we owe a great deal to these microorganisms. And not just our oxygen, when they die, their silica frustules
sink to the bottom of the water that they're in and accumulate into a soft, chalky rock that
we know better diatomaceous earth. That key ingredient in beer and wine filtration,
paint, and of course, cat litter. So, yes, these beatufiul jewels that the unknown Mr. C spotted in 1703 don’t just provide us with every fifth breath we take, they also
help make our cat litter more absorbent. And also, they’re just really nice to
look at. So thank you for coming on this journey with us as we explore the unseen world that surrounds us. If you want to see more from our Master of Microscopes, James check out Jam and Germs on Instagram. And if you want to see more from us, there's always a subscribe button somewhere nearby.
The PI for one of my labs was a world-renowned diatom expert, so I’ve spent an inordinate amount of time boiling them in acid so they’re nice and pretty on a slide. I still really enjoy them.
One of her specialties was reconstructing ancient climactic records by analyzing the population of diatoms embedded in the lake cores of high Amazonian lakes. In El Niño seasons, for example, the change in water would lead to a change in the frequency of diatom populations.
Thus you can actually track the development of certain weather systems by looking at the fossil record and compare that to frequencies today.
I've really been enjoying this show, I'd like to see the diatoms separating daughter cells and repairing their shells. Also would like to see a new full size shell being created, I haven't seen any silicon based cells before this.