How Stressed Algae Curl Into Protective Cysts

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[00:00:26]This algae is stressed. And we can tell it’s stressed because it’s doing something that you  might also do when you find yourself in a difficult situation. It’s turning red. But while blushing brightly for everyone to see might make your situation worse, this  algae can do something else that sounds, honestly, very appealing: it can curl up in  a ball and just wait out the worst of it.

[00:00:51]This algae is called Haematococcus, and  it is not, physiologically speaking, turning red through the same mechanisms that  you and I do when we are stressed and blushing.

[00:01:02]We flush with blood. Meanwhile, the Haematococcus  does not have blood. But depending on the state of your ancient Greek, you might recognize its  name translates loosely to “blood berries,” a name that seems fitting for a  round, reddish organism like this one.

[00:01:20]But as poetically sanguinary as the name is,  Haematococcus flushes with something else altogether, a chemical we can see traveling  through the algae and up the food chain, until it winds up on our own plates. But before we get to the dinner table, let us talk about where we got our Haematococcus:  from a centuries old cemetery in Warsaw, Poland, filled with beautiful sculptures and birdbaths. For James, our master of microscopes, it is important to respect the tombs there. So, don’t  worry, these microbes don’t have particularly spooky origins. He’s there for the birdbaths,  where the algae lines the surfaces like rust.

[00:02:07]The Haematococcus likely arrived at the  birdbath thanks to the birds themselves, and there it would have remained until maybe  another bird came along, except this time, your favorite microbe hunter came first. In addition to birdbaths, Haematococcus are often found in transient pools of freshwater,  like puddles after a rainfall. And as you can see on your screen, not all Haematococcus are  red. Plenty of them are green, which makes sense because Haematococcus is a member of the phylum  Chlorophyta and that phylum is full of many other unicellular green algae like the volvox. And as algae, Haematococcus are green, photosynthetic, and very easy to eat, which makes  them a simple solid foundation for an ecosystem.

[00:02:56]But even seemingly simple creatures  have requests of the world around them, whether that’s for certain levels of light, or a  particular temperature. And if you were to say, go to a hotel and your room was 100 degrees,  you got a few solid options to fix that problem.

[00:03:12]You could find the thermostat. And if that  doesn’t work, you could complain to the manager or even just go find another place to stay. But those are not great options for the Haematococcus. There’s no thermostat to  change, there’s no manager and if the temperature gets too high, there’s only so  much a single-celled body can do to survive.

[00:03:33]So instead, the Haematococcus does what I’m  sure many of us wish we could do when we were in an uncomfortable situation: it takes  a little bit of a break, forming a cyst that allows it to rest and survive  until conditions are good again.

[00:03:48]When you’re looking at this mixture of  Haematococcus, you’re looking at a gathering of algae in different phases of their lives.  The most active ones are called macrozooids, or zoospores. They might be shaped like spheres,  ellipsoids, or even pears. And they’re encased in a thick gelatinous wall, with two flagella  extending out in front to zip the algae around.

[00:04:11]But most importantly, here at  this stage, the algae is green.

[00:04:15]The Haematococcus rarely reproduces sexually,  and when it’s a macrozooid, it divides rapidly, forming around 2 to 32 copies of itself. But  it makes sense to move around and make more of yourself when conditions are good. What happens  though when you’re in a comfortable pool of water one day, and in much more dire straits the next? Well, for the Haematococcus, this is the point at which it all begins to change. The algae  sheds its flagella, layers up its wall, and shifts into a ball. This is the  Haematococcus as a palmella, a resting cell.

[00:04:53]But if stress has taught me anything,  it is that things can always get worse.

[00:04:57]And for this little cell, it can get hotter or  saltier or just too bright. And when that happens, the palmella morphs into an aplanospore.  Its walls become even heavier duty, shielding it from the outside. But most striking,  this is when the haematococcus becomes red.

[00:05:15]The red is practical, the product  of a chemical called astaxanthin.

[00:05:19]Astaxanthin is a carotenoid, a type of reddish  yellow pigment found in plants and microbes. But it’s more than just a pretty color. Astaxanthin  is an extremely powerful antioxidant, protecting the cyst from potential damage as it rests. You’ve probably seen astaxanthin in real life, except you might not have  called it that. You might have just called it “pink,” or “salmon pink.” Astaxanthin is found in plants, fungi, bacteria, and yes, in algae. And haematococcus, is  considered to be one of the best natural producers of astaxanthin, able to produce up to 5% of its  dry weight in astaxanthin. For comparison, another astaxanthin-producing algae called Chlorella makes  around 0.001% of its dry weight in astaxanthin Now the reason we find astaxanthin  in so many animals is because, algae make for good food, whether you  are a shrimp, salmon, or flamingo.

[00:06:18]It’s striking that the color we call “salmon  pink” is a sign of both the salmon’s contentment and the algae’s demise. Perhaps we should start  calling it “haematococcus pink” instead, an acknowledgement of the work of the haematococcus,  which endures so long after its death.

[00:06:38]It would be a fitting tribute after all to a  color you might have eaten a few times yourself.

[00:06:43]The salmon, sure, which might have fed on  synthetic astaxanthin or algae. But even the chicken eggs you buy might have gotten their  yolk color boosted by algae added to chicken feed.

[00:06:55]Astaxanthin has its uses outside of our food,  whether in our cosmetics or nutraceuticals.

[00:07:01]And while much of that is synthetic, a copy we’ve  learned to make by studying the chemistry of astaxanthin, there’s also a push in the market for  “natural” products, a push that has led to renewed interest in the haematococcus algae and its  wondrous ability to produce its own astaxanthin.

[00:07:19]But for the haematococcus that’s just something  weird going on in the outside world, a factor far beyond its control and its interest. Whatever  comes its way--whether it's a scientist, a bird, or a fish--all the haematococcus is concerned with  is its own survival. What belongs to the algae will one day belong to another organism, passed  on through chemistry and made into something new Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.

[00:07:53]And thank you again to Babbel for sponsoring  this episode of Journey to the Microcosmos.

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