If, for some reason, you ever find yourself  reading a bunch of papers about cryptomonads,   you might come across this strange  fact: they have four genomes.

That sounds like a lot of genomes. But what exactly does that even mean?

And what does the cryptomonas  do with all those genomes? The genus Cryptomonas was introduced in 1831  by the prolific microbiologist  Christian Gottfried Ehrenberg. They’re mostly greenish brown  in color, and in nature, green   is often associated with photosynthesis  and the various pigments that drive it.

And many cryptomonads are photosynthetic,  using chlorophyll and accessory pigments that   are packaged in photosynthetic  organelles called plastids. But there are also several cryptomonad species  that are no photosynthetic, like the colorless   cryptomonas paramecium frantically dancing  around the giant blepharisma in this clip. You might expect that this means the  Cryptomonas paramecium doesn’t have plastids.

It isn’t performing photosynthesis, so what need  would it have for a photosynthetic organelle? Well... Plenty, it turns out.

To understand why, we've got to look into how  the cryptomonas got its plastid to begin with. In some ways, it’s a standard tale  of endosymbiosis in the microcosmos. At some point in the past, an ancestor  of cryptomonas consumed a red algae.

But instead of fully digesting it for food,  the organism kept bits of the red algae around— namely, the algae’s plastid. Interestingly though, the red algae’s plastid  is itself the product of endosymbiosis,   a similar tale involving some ancient  ancestor, only it had likely consumed   a free-living cyanobacteria that it  eventually converted into a plastid. So the red algae plastids are the product  of what’s called primary endosymbiosis,   and cryptomonad plastids are the result  of what’s called secondary endosymbiosis.

And on top of co-opting the red algae’s plastid,  the cryptomonas ancestor also took the red   algae’s purple pigment phycoerythrin  to power the photosynthesis. But plastids are not the only example of  endosymbiosis contained in cryptomonads. The other one is a trait that  cryptomonads share with us and   almost all other eukaryotes: the mitochondrion.

And this is why the cryptomonad has four genomes. The first is its own nuclear DNA,  the foundation of its identity. The second is its mitochondrial DNA, a remnant  of DNA of an essential energy-producing organelle.

The third is the plastid DNA from the red algae. And the fourth? The fourth sequence of DNA is a weird one.

It’s called the nucleomorph, and it’s like a  version of the red algae’s nucleus but just…less. This makes cryptomonads different from  some other eukaryotes that have developed   organelles through secondary endosymbiosis  because those other organisms have managed   to lose the nuclear remains of  their endosymbiont altogether. And different is exciting when you are a scientist.

In this case, it makes cryptomonads useful  to those who want to learn more about the   diverse paths endosymbiosis takes as  it converts organisms into organelles. Returning to our Cryptomonas paramecium, for  example, scientists have looked into why the   species would keep plastids around when  they don’t use them for photosynthesis. But plastids are able to do more than  just photosynthesis, it turns out.

At least, when scientists studied the plastids  in Cryptomonas paramecium and several other   non-photosynthetic cryptomonads, they  found that the plastids were able to   make fatty acids and amino acids and carry  out a number of other important reactions,   though actual functions a plastid might  serve can vary from species to species. Despite their intrigue, cryptomonads are  also challenging to study for a few reasons. For one, they can be a challenge  to collect and keep alive.

James, our master of microscopes, said  that they tend to die very quickly,   seeming to disintegrate as soon as he  looks at them under the microscope— though he has found that the  non-photosynthetic ones are a little hardier. But in addition to the difficulty  of keeping cryptomonads,   they’re also really hard to tell  apart using light microscopy. The features that distinguish species are  just too muddied and difficult to categorize.

But microbiologists are resourceful,  and since the end of the 19th century,   they’ve been working to isolate and maintain pure  cultures of algae that can provide scientists   with the uncontaminated specimens they need  to better understand the microbial world. One of these scientists was Ernst  Georg Pringsheim, a German scientist   who first began publishing papers  on how to culture algae in 1912. He refined techniques that allowed him  to pick up single cells with a pipette,   and figured out the quality of water that  would best allow his cultures to survive.

In 1922, he had moved to Prague to carry on his  work as professor and develop his algal cultures. And while there, he met Olga Zimmerman, a student  who would become his frequent collaborator. Pringsheim was offered a position that  would allow him to return to Germany.

But he was Jewish, and  Hitler was coming into power. So instead Pringsheim and his family  left Prague for England in 1938,   right before the German  occupation of Czechoslovakia. And even with the turbulence of war around him,   Pringsheim brought some of his  algae strains with him to England.

And he maintained them, keeping them  going so that when he did return to   Germany in 1953, he could use them  to establish cultures there as well. In fact, even after his death,   Pringsheim’s cultures have served as the  basis for more than 400 algae cultures   distributed across collections maintained  at various institutions around the world. And they’re still being used for research and  teaching today.

Just this year, a group of   scientists reported the results of their work  studying a particular strain of cryptomonads   whose origins lie in a Pringsheim culture that  scientists have continued tending to for decades. When scientists looked inside this particular   strain, they found two bacterial  endosymbionts and a bacteriophage— or bacteria-infecting virus— also living inside the Cryptomonads. Their work revealed an expanded  world within this particular strain. (And if you’re counting, this strain  of Cryptomonas has seven genomes) We don’t know yet how the relationships  between these organisms work,   but the fact that this grouping  has persisted through around 4000   generations of this strain suggests  that it is probably very stable.

It is a little odd to describe the world within these   strains as “stable” when the world  that produced them was anything but. It’s also hard to adequately place meaning  and value to Pringsheim’s commitment to his   cultures in the context of the antisemitism  and war that shaped his life and work. And yet it is a wonderful thing to leave  a legacy built on care and curiosity.

It is a legacy that sustains itself by  training the next generation in its methods,   and providing the vessel for new questions. It leaves a mark on this world, as enduring,   you might say, as an ancient  genome buried in a cryptomonad. Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.

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