Thor. Loki. Heimdall. They're not just Norse gods or Marvel characters. They're also the names of various Asgard archaea. These microscopic organisms are found all over the world, from marine sediment to mud volcanoes to hydrothermal vents. A growing body of research suggests we owe them an evolutionary debt. This episode, Emily and guest host Jon Hamilton explore the wild world of archaea: Where are they from? What do they do? And what can they tell us about the origins of life on earth? Interested in more stories about life's origins? Email us at [email protected]. We'd love to hear from you!Learn more about sponsor message choices: podcastchoices.com/adchoicesNPR Privacy Policy
Chapter 1: Who are the hosts of this episode?
You're listening to Shortwave from NPR. Hey, short wavers, it's Emily Kwong here.
And John Hamilton.
With a story that kind of picks up where Regina and I left off in November. So, John, do you remember the episode we did about hydrothermal vents and the origins of life?
Oh, how could I forget? The two of you were getting at this idea that maybe the building blocks for life, you know, nucleotides, amino acids, were created around those super hot vents on the ocean floor.
DNA and RNA, for example, are extremely vulnerable to, like, UV light. So maybe they first formed deep in the ocean where they'd be protected from those rays. That's amazing.
I mean, sounds plausible to me.
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Chapter 2: What are archaea and why are they important?
Right?
And it left me with so many questions. Like, where did life go from there? You know, what's the next chapter, the moment where that molecular bath gave rise to discrete life forms, to single-celled organisms? Perfect. And eventually to complex multicellular organisms like you and me, eukaryotes. And there's this one type of life form that I think is key to telling that story, John.
Have you heard of archaea?
Or archaea, as some say. Tomatoes, tomatoes.
Both pronunciations are fine. But do you know what they are?
I do, but only because years ago I happened to run into a biologist who studies them. I have never seen archaea in the wild.
It's not your fault. They are tiny. Tiny. Even under a high-powered microscope, the largest archaeans look like tiny dots. But if you zoom in closer, you'll see they possess all kinds of shapes. They're spheres, they're rods, they're spirals. They look like bacteria, but they're not. And despite having no nucleus, no organelles, I think these overlooked microbes have main character energy.
So today on the show, we're going to give archaea their due.
how our microbial ancestors gave us our mighty immune system, are at the center of one of the biggest ideological battles in biology, and are connected to the legend of Thor?
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Chapter 3: How did Carl Woese revolutionize microbiology?
The way evolutionary biology had been done in the organismal side of this world was to look at traits that change over time, you know, butterfly wings and plant leaves and seed colors and the beaks of the Darwin's finches and things like that. And that's really hard to study when you're looking at microbes because there's no traits.
I mean, they do have different shapes and they do have different surface structures and stuff. But back in the day when we were just discovering microbes, that was really hard to even say how they were related to each other.
And Woese said that physical properties are not a reliable way to tell those relationships. He really pushed for a molecular approach. This was back in the 1970s.
People were starting to use molecules, amino acids and RNA. They were starting to use those as signatures of evolution.
For him, one molecule that was found all over the map was the ribosome. That's the machine that turns RNA into proteins. He began to study RNA sequences using these giant films of gel. and cataloging their differences, tracing how they evolved over time.
He had these notebooks and notebooks and notebooks, and I've seen these notebooks. There's like shelves of them, which are basically saying the size of each of these little bands in these two-dimensional gels is And based on that, he was finding relationships.
And then, right down the hall, his colleague Ralph Wolf found these weird microbes at the bottom of the food web responsible for the greenhouse gases in cows. These microbes, they were single-celled. They kind of looked like bacteria, but also kind of not.
Until he walked down the hall and said to Carl, well, you should really look at these guys. They're very different. I don't know what they are.
And because Woese had developed this molecular tool for comparing RNA sequences, he could use it on these mystery microbes. And he determined they were not bacteria. They had different cell walls. Their RNA was more similar to eukaryotic RNA.
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Chapter 4: What are the main differences between archaea and bacteria?
All right, I'm getting the theme here. Asgards, Loki, Norse mythology.
Correct, yes. And after the discovery of these Loki archaeota in 2015, Brett says...
And we found this other group that was related to it. So we called it Thor. We collaborated and found a bunch more groups and Odin and Heimdall.
Ever since, Brett's team and others have been sequencing the genes of these Asgard archaea found in hot springs, aquifers, freshwater, saltwater environments around the world. And what they found has challenged the work of Carl Woese and the story of how life began.
How so?
Okay, so these Asgard archaea, their genes are actually really similar to eukaryotes. And then, Brett told me... which suggested something that went beyond Woese's work. It suggested that eukaryotes, like trees, mushrooms, birds, us, all the cool kids, may have in fact come from Archaea, that the eukaryotic branch in fact sprouted from some ancient Asgardian ancestor.
I literally went running into my grad student's office and I said, oh my God, we have something very big here.
And at the time, this was very controversial. But Brett and other researchers kept doing the work and standing up to the naysayers, saying, no, this is right.
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Chapter 5: Where can archaea be found in extreme environments?
Chapter 6: What does the future hold for archaea research?
Okay, so these Asgard archaea, their genes are actually really similar to eukaryotes. And then, Brett told me... which suggested something that went beyond Woese's work. It suggested that eukaryotes, like trees, mushrooms, birds, us, all the cool kids, may have in fact come from Archaea, that the eukaryotic branch in fact sprouted from some ancient Asgardian ancestor.
I literally went running into my grad student's office and I said, oh my God, we have something very big here.
And at the time, this was very controversial. But Brett and other researchers kept doing the work and standing up to the naysayers, saying, no, this is right.
Eukaryotes actually fall within the archaea. We are literally Asgardian. Obviously, it's two billion years of evolution since we evolved from them. But they are our ancestors.
And new research is continuing to bear this out when it comes to the story of how our immune system evolved.
So bring us up to date. Give me some specifics here.
So a few years ago, another microbiologist, Pedro Leal, who's from Brazil, came to work in Brett's lab at UT Austin as a postdoc. And Pedro was reading about how certain proteins that helped our ancient immune system do its job may have come from bacteria. Yes.
And me, as someone working in the archaeal side of the origin of eukaryotes, I was like, why someone is focusing one in one player that formed the eukaryote and not a second one? I know archaea play a role in this.
He was like, why are they not looking at archaea? Why are people always forgetting about archaea? And he wanted to look for evidence that archaea may bear clues for how our immune system evolved.
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