Mysterious Jiggly Crystals and Other Intracellular Structures

When you peer into the microcosmos, it’s
sometimes hard to see past the cells themselves. Flitting around, fighting, surviving, movement
and shapes and colors. But we can see deeper, and there is so much
to see if you look beyond that first level, and into the cell itself. In the cytoplasm, mysteries and curiosities
abound. Here in our macro-world, to see inside an organism we need expensive scans or exploratory surgeries. In the microcosmos, we can just turn on the
light and see some of the bizarre and beautiful systems that these organisms have for increasing
their chances of surviving a harsh and uncertain world. So let’s take a look at some of the structures
inside of cells that you may have never heard of, and that we love to let blow our
minds. This is the unicellular alga Closterium. And at the very tips of the cells, an alluring
little object. Do you see that orb with the tiny round things
inside? Those are actual crystals made of barium and
calcium sulfate. But why are they there? Well, no one knows yet, and we hope…nay
we know… someone will someday solve this mystery. But for now, it is yet another thing that we do
not know about our universe. These crystals are extremely small. Around two to three microns across. If you divided a milimeter into 500 equal
pieces, one of those pieces is how big those little grains are. But there’s more. You see how those crystals jiggle around and
never stop moving, even though nothing seems to be moving them. Well, one thing we know about the universe
is that things don’t just move….the energy has to be coming from somewhere. Let’s remember that everything you’re looking at here is made of atoms. And when two hydrogen atoms and one oxygen
atom come together, they form a water molecule. Now, Closterium lives in water, which means
it’s surrounded by and filled with water molecules. And they are in constant motion, that’s what heat is. The movement of atoms and molecules. If they weren’t moving at all, that would
be absolute zero. -273.15 degrees Celcius. That’s not where we’re at. These water molecules are moving around a lot and they’re bumping into
everything and they can even move objects around. But if something is really big, like a whole
Closterium cell, you can’t actually see any movement. But since these crystals are tiny, the water molecules visibly toss them around. This dancing is called Brownian
motion, and we love it because we of course cannot see water molecules under the microscope, but we can observe their effect on these crystals. Indeed, Albert Einstein used brownian motion
to confirm that atoms and molecules exist which, in 1905 when he published his paper
on the subject, was still a matter of debate! And now, we’re watching it happen…watching
water molecules smashing around into crystals that, as yet, remain unexplained, but must have some reason to exist besides being fun for us to look at. This is Nasulla ornata, a beautiful unicellular
ciliate. Although it doesn’t look like it right now,
they can move quite fast. But what you are looking at is a squashed Nassula ornata. We decided to give it a bit of a squeeze so we could take a real good look. When Nassula ornata hunts for food, It prefers filamentous cyanobacteria or algae It wraps its membrane around it, forming a food vacuole. As it continues to eat it forms more and more of these vacuoles. Now, what’s so nice about them are their colors. Cyanobacteria and algae, Nassula’s food,
are green, but when Nassula starts dumping digestive enzymes into these food vacuoles, a chemical reaction occurs changing
the color of the food vacuole over time. Because different vacuoles are at different
stages of digestion, each vacuole is a slightly different color, giving this ciliate its beautiful, colored polka dots. These are the very long, very skinny cells of the filamentous sulfur bacteria Beggiatoa. You can find them all over the globe living
in habitats from marine caves to sulfur springs to everyday ponds and rivers. When we find them, they are usually on freshwater
pond sediments or decomposing organic material. Beggiatoa excretes mucus, which allows them to glide around on the sediments. Beggiatoa prefers sulfur-rich environments
because they oxidize hydrogen sulfide as an energy source. The hydrogen is used by the organism in chemical synthesis, and the sulfur is left over. Every one of those tiny black dots that you see is a granule of inorganic sulfur. Here’s another clip where you can look at
them a bit closer under 1000 times magnification. Which, for the moment, is about as good as we can do here. Now, what’s happening here…these little
bubbles forming and popping…well they are not bubbles of air, they’re bubbles of pure
water. One of the most fundamental structures for
life as a freshwater single-celled organism is the contractile vacuole. This organelle allows unicellular organisms
to pump excess water from their cell. Why? Well, Inside of every cell, there are a lot
of dissolved substances—more than the surrounding water contains, certainly. Whenever there is an imbalance like this, things
tend toward equilibrium. And the only thing separating these cells
from the water around them is a membrane that allows some, but not all substances
to pass through it passively. One of those substances is water. When the concentration of stuff inside the
cell is higher than the concentration of stuff outside, water diffuses into the cell. There is no way to stop this diffusion. The solution to this constant influx of water
is the contractile vacuole. This organelle fights a continuous battle, pumping and pumping and pumping the water out. Imagine, though, if the contractile vacuole
was not working. You might think that, eventually, the cell
would fill with so much water that the cellular machinery might break down. Well, maybe, except, before that happened,
the cell would expand so much that its membrane would break and it would literally explode. So, y’know, good job little vacuole. The ciliate Loxodes is a common resident of
different aquatic habitats, but they prefer a distinct zone in the water. A “Goldilocks” zone for oxygen. They like concentration not to be too
high and not too low. And in a body water, unless something weird is
going on, the oxygen concentration is higher at the top and lower toward the bottom. Because of its specific oxygen concentration
preference, Loxodes needs to know which way is up and which way is down so it can find
just the right spot. But how could a single celled organism know
up from down? Well, Loxodes can sense gravity! It has organelles called Müller vesicles
that each contain a spherical mineral granule—the Müller body—attached to a hair-like cilium. Sorry these friends zip around so quick, it
can be hard to get a good look. These granules, the Müller bodies are actually pulled down by gravity, and it is believed that this “pulling” causes sensory signals to be transmitted to
the cell through the cilium. So, Loxodes, despite being tiny and despite being just a single cell, has an organ very much like our inner ear, allowing it to sense
up from down. So yes, microbes display quite the collection
of intracellular structures! Only a few of which we discussed here. Some shiny, some colorful, and some that provide
fascinating advanced capabilities. And it makes us wonder, what other structures are yet to be discovered? There is so much that we do not know. We hope to report back to you on this question
because we are sure that there are many more out there just waiting to be unveiled by a
discerning eye peering into the microcosmos. 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 here at Journey to the Microcosmos, I bet there’s a subscribe button somewhere nearby.


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