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Oomycetes are one of the more unusual-looking microbes we’ve seen in the microcosmos. It looks more like a coral reef painted by an artist inspired by Gustav Klimt and a pile of trash. And if you saw that painting hanging in the museum, you might pass it by without thinking much of its subject.

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Stock video from:
https://www.gettyimages.com/detail/photo/potato-royalty-free-image/923237822
https://www.gettyimages.com/detail/photo/tomato-on-branch-affected-by-late-blight-or-royalty-free-image/1362440235
https://www.gettyimages.com/detail/video/crazy-scientist-stock-footage/151348385
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SOURCES:
https://www.parliament.uk/about/living-heritage/evolutionofparliament/legislativescrutiny/parliamentandireland/overview/the-great-famine/
https://www.britannica.com/event/Great-Famine-Irish-history
http://www.plantpath.cornell.edu/Fry/
https://www.frontiersin.org/articles/10.3389/ffgc.2021.668895/full
https://www.astacology.org/MeetingPresentations.asp?uid=guest&s=21&t=1&ln=B
https://www.apsnet.org/edcenter/disandpath/oomycete/introduction/Pages/IntroOomycetes.aspx
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC154851/
https://kids.frontiersin.org/articles/10.3389/frym.2021.560315
https://ucmp.berkeley.edu/chromista/oomycota.html
https://www.cell.com/current-biology/pdf/S0960-9822(06)02054-9.pdf
https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1004805
https://www.frontiersin.org/articles/10.3389/fcell.2020.00229/full
https://www.pnas.org/doi/epdf/10.1073/pnas.1105100108
https://academic.oup.com/femsre/article/35/3/542/541837
https://www.cell.com/heliyon/pdf/S2405-8440(21)00422-9.pdf

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Have you ever been watching a movie or a TV show and you saw an actor doing a thing that you know a lot about and they are just not doing it right?

Well, we have and that thing we know a lot about is microscopy. And there are plenty of examples out there of movies and TV shows that get microscopy right, and then there are others that show a scientist looking through a microscope that has no objectives attached to it.

And yes, that's a real example of something we've seen in a TV show. But instead of just sitting there, wanting to shout at the screen, we have decided that, exclusively for our Patreon patrons, we’re going to record a Microcosmos Reacts video where some members of our team will be reacting to some good and not-so-good movie microscopy. But we will only make this video if we hit our current goal of 900 monthly patrons!

So, if you would like to support this channel and help us hit our goal so we can make that video, you can head on over to patreon.com/journeytomicro. And please let us know in the comments below if you have any favorite movies and TV shows that have done microscopy either really well or really bad. The organism here is one of the more unusual-looking microbes we’ve seen in the microcosmos.

In fact, calling it an organism seems strange. It looks more like a coral reef painted by an artist inspired by both Gustav Klimt and a pile of trash. And if you saw that painting hanging in a museum, you might pass it by without thinking much of its subject.

In the middle of the 19th century, an organism that looked a bit like this one did a terrible thing. It could not know that it was doing something terrible of course. It had recently arrived in a new land, and all it sought was some food.

But in the process, it starved a nation and killed many people. The organism was a type of water mold called Phytophthora infestans, which made its way from North America to Ireland. And with its arrival came the Great Famine.

Phytophthora infestans infected potato and tomato plants, producing lesions on the leaves and stems, and appearing as a white growth along the lesions. The infected crops rotted, making them inedible. Phytophthora infestans belongs to a group of organisms called oomycetes, which translates to “egg fungus.” And we’ve actually encountered another destructive member of this family before, early in our journey through the microcosmos.

We recommend going and watching that video because it’s still one of the oddest events we’ve watched unfold under a microscope. But what we’ve learned since then thanks in part to oomycete expert Bill Fry from Cornell University, is that we were watching a parasitic oomycete that had managed to turn a Daphnia’s egg into its own vehicle for reproduction. On the rare occasion that we find oomycetes in our samples, it’s almost always under similar grim circumstances, where these strange creatures have found a way to grow on the bodies of dead bugs or crustaceans.

And we’re never entirely sure if they just happened to stumble on a dying organism to feed on, or if they were actually the cause of death. Now, there are free-living oomycetes that don’t infect other organisms. Instead, they feed on decaying life.

But as for the rest: an oomycete researcher named Gordon Beakes once gave a talk titled “natural born killers”. And if you go through a list of oomycetes, you start to realize just how well-earned that name is. There’s Aphanomyces astaci, which has wiped out populations of European crayfish.

There’s Phytophthora ramorum, which took down oak trees in California. There’s grapevine-targeting Plasmopara viticola, the maize-infecting Peronosclerospora philippinensis, the list goes on and on, affecting everything from soybeans to chocolate production. And none of this sounds that out of character for a group of organisms collectively called “egg fungus,” right?

There are fungi that like to eat dying things, and there are fungi that like to infect plants. We’ve even witnessed murderous fungi at work here in the microcosmos, weaving their web around unsuspecting nematodes. So oomycetes are just one more of these fungi, their filamentous structures helping them spread their bodies as they prepare spores that will help them spread even further.

Except, oomycetes are not fungi. Their walls are not made of chitin the same way fungi walls are, and their nuclei have two copies of genetic information compared to the fungi’s singular copy. Instead, it turns out that oomycetes are members of a different group of organisms called Stramenopiles, making oomycetes more closely related to diatoms and brown algae than they are to fungi.

And it’s strange to think about it in these terms. Diatoms are about as close as you can get to pacifists in the microcosmos. They enclose themselves in silica walls and photosynthesize to make their own food.

It’s like oomycetes are killers turning up to a family reunion full of hippies who spend their days churning sunshine into sugar. You can’t help but look at them and ask, “How did you turn out like that?” Well this certainly wouldn’t be the first time two very unrelated organisms share an uncanny resemblance. Birds and bats and bees all have wings, but the wings do not make them closely related.

These animals just went through their own histories of adaptation and survival, and in the process converged upon the same idea. And there’s probably some degree to which oomycetes and fungi experienced something similar. They both happened upon a form and lifestyle that parasitized and infected, profiting on the decay that results.

But at some point, something strange happened. The supposedly-parallel paths of oomycetes and fungi intersected, sparking collaboration. Or rather, oomycetes copied fungi.

The process by which oomycetes did this is called horizontal gene transfer, which allows genetic material to move from one organism to another through some means that is not reproduction. It’s pretty common in prokaryotes, but as scientists have learned through oomycetes, eukaryotes can go through horizontal gene transfer as well. As part of our ongoing battle with oomycetes, scientists have had to get well-acquainted with their genes.

And as they studied these sequences, they found that some of the species, particularly the plant-infecting species, had genes whose origins had to have come from fungi through horizontal gene transfer. In Phytophthora ramorum, the oomycete that kills oak trees, scientists estimated that 7.6% of the proteins released by the organism are produced from genes that originally came from fungi. Some of these copied genes have given oomycetes the ability to break down plant cell walls.

Others may help the oomycetes combat plant defenses. Based on our look through the research on horizontal gene transfer from fungi to oomycetes, it’s not clear what the process actually looks like. That information makes horizontal gene transfer seem like some arcane biological magic, bringing together two organisms that superficially resemble each other and making them related without making them family.

Meanwhile, in the world around us, spores spread and take hold of dead insects and soon-to-be-dead plants. And buried in their bodies is the evidence of the unusual collaboration that has made them so deadly, an incomplete answer to the question, “How did you get this way?” Thank you for coming on this journey with us as we explore the unseen world that surrounds us. If you’re interested in fungi that’s a little less micro, you should check out this video from our sibling channel PBS Eons, all about the giant, ancient fungi that once ruled the world.

And while you’re over there, you should also subscribe and check out the rest of their videos, where they will take you on a journey through the history of life on Earth. You can find the giant fungi video, and much much more at youtube.com/eons The folks on the screen right now, they are our Patreon patrons. They're the people who make it possible for us to make this show.

And also they've gotten us almost all the way to 900 patrons. And when we get there, we will make that video reacting to wonderful and terrible screen microscopy. So they've gotten us most of the way there.

But if you want to help get us all the way there, you can do that by going to patreon.com/journeytomicro. If you want to see more from our master of microscopes, James Weiss, you can check out Jam and Germs on Instagram. And if you want to see more from us, there's probably a subscribe button somewhere nearby.