Cells divide, and in the process they create duplicates of single-celled organisms or they
fill out the bodies of multicellular life.
It’s a process without which life as we know it could not exist, it sustains individuals
and species alike.
And on Journey to the Microcosmos, we’ve been privy to this vital sequence quite a lot.
At times, the division looks a bit like this, two cells in the middle of pulling apart from
each other.
Or maybe they look a bit like these spiky guys, clearly ready to move on to the next
stage of their lives apart from each other.
Except…these are not examples of cell division.
What you’ve been watching are not two single-celled organisms undergoing the last steps of what
will finally separate them.
No, this is one cell, belonging to the order of desmids, a type of green algae that takes
symmetry and beauty to a new and sometimes mysterious level.
There are thousands and thousands of species of desmids, and the ways they exhibit their
symmetry varies accordingly.
Sometimes they repeat a more rounded shape.
Other times, the microscopic mirror creates more of a crescent or rod shape.
The underlying composition, however, follows a blueprint.
These freshwater microbes are unicellular, though some species form long-chained colonies.
Each desmid cell is made of two symmetrical halves, or semicells, connected by a thin
region called the isthmus that also holds the cell’s nucleus.
That word, isthmus, of course, is from geography, a narrow strip of land that connects two larger
pieces of land.
Inside this Micrasteria are, as you might tell from the green color, chloroplasts.
But there are only two of them—each one large and knit into the various nooks and
crannies of their respective semicells.
It’s remarkable to consider just how green one or two chloroplasts can be—just take
a look at this dead Micrasterias for contrast, the vivid color gone with the rest of its
life-giving processes.
Less elegant in theory, but—as with everything they seem to do—striking to observe, many
desmids release a gelatinous substance from their pores.
This secretion forms a mucilaginous cell layer around themselves, which acts as a boundary
that might help keep the cell protected or might function to trap nutrients.
Even now, we’re not sure.
We started off today comparing desmids to dividing cells, and maybe even trying to trick
you into confusing the two.
But desmids do also divide.
Well, sometimes they actually reproduce sexually through conjugation.
But in observing its asexual reproduction and cell division we can find an important
(though invisible) difference between desmids and the otherwise similar semicells: their age.
Desmids divide at the isthmus, separating the two half cells that then have to grow
out a new semicell.
This means that within each desmid, each half cell might be different ages.
You might very well be looking at whatever the green algae semicell equivalent of an
adult is, conjoined through the isthmus to its younger mirror.
It's like having half of your body be a child.
Desmids aren’t unique in having some kind of symmetry—we see symmetry all across nature,
to the extent where asymmetry might revealmore about how an organism works than symmetry does.
But this kind of mirrored, semicell arrangement is particularly striking to look at and to consider.
Which leads, naturally, to the question…why?
We haven’t yet dug up any scientific literature that can explain what advantage this symmetry
might provide, though of course we might also be seeking the simplicity of easy evolutionary
answers when reality is more complex.
But if you do have an answer or even just a guess, let us know because at the moment
we don’t have any.
Symmetry, however, is only one part of what makes desmids so striking to look at.
Most desmids have these strange crystals inside of them.
The crystals are tiny, and their paths are impacted by the movement of individual water
molecules that fill up the cell and collide into those crystals, creating frantic movements
that is also known as Brownian motion..
As we shine polarized light on those crystals, we can see them dancing and lighting up the
green around them as if it’s a holiday season in the microcosmos.
But what are the crystals for?
They have to be for something.
But again, we do not know.
Microbiologists are still working to figure it out.
But whatever specific need they are filling, these crystals may play a role in parsing
through a big chemical question: how do we clean up radioactive waste?
Now, this might not be a question you’d expect to be answered in the form of Closterium,
a desmid that looks a bit like a green banana.
But Closterium collects barium from its surroundings.
As the barium gets shuffled into the Closterium’s sulphate-rich vacuoles, it precipitates into
crystals, which you can see compartmentalized but still moving in the tip.
Again, these crystals are mysterious—we don’t know what purpose they serve, or if
they even serve a purpose.
But in studying them, scientists have observed that under certain conditions, Closterium
moniliferum can collect strontium from the water and, within 30 to 60 minutes, precipitate
it in the very same vacuoles that it uses to create its barium crystals.
This talent might be a handy one to have when, say, you’re tasked with selectively clearing
out radioactive strontium-containing water following a nuclear disaster.
However, we wanted to note that the experiments demonstrating that Closterium can take in
strontium were not designed to test to see how well the organism can handle radioactivity,
so while it can definitely pick up strontium, it might not be happy picking up radioactive strontium.
So, the application here, still a hypothetical.
Scientific caveats aside, it’s tempting to fully indulge that train of thought, and
to envision a world where microbes save us from ourselves.
After all, these are organisms whose own symmetric morphology imply order, even as they house
the random motion of mysterious, jittery crystals.
But whether desmids serve to help us contend with future disasters or not, their striking
shapes and structure provide us with another service, the simple beauty of the microcosmos.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you especially to all of these people who make Journey to the Microcosmos possible
by supporting us on Patreon.
If you want to see more from our Master of Microscopes, James Weiss, check out Jam and
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