Chapter 1: What is the main topic discussed in this episode?
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in a New Mexico cave. Microbes are doing photosynthesis in total darkness, which sounds impossible until it rewrites what we think life needs to survive. And then a conversation starts about where in the universe life might be hiding. We're here with someone who has researched this weird, wacky life. His name is Lars Behrendt.
He's a microbial ecologist at Uppsala University and the Technical University of Denmark. Lars, welcome to the show. Thank you so much, David. You go to a cave, you shine a flashlight, and then you see it glowing green. What do you think?
Chapter 2: What unusual microbes photosynthesize in the dark?
You think someone's down there playing around with glow-in-the-dark stuff, or you're on to something very strange in the world of biology?
Yeah, both, I think. So, I mean, I was really excited when you kind of can test your hypothesis as a scientist and suddenly you think you might have actually found something. So we went down into these caves based on some research that I did earlier in my PhD. And this was on, you know, kind of very special type of photosynthesis that we thought obscure.
And we looked around different places and eventually we stumbled into caves. And yeah, there it was, lo and behold.
Look, I took biology in high school. I did badly in biology in university. When I hear photosynthesis in total darkness, I think that's a contradiction.
Chapter 3: How do these microbes challenge our understanding of life?
Don't you need sunlight for photosynthesis?
Yeah, I think maybe what we need to define is a bit light, right? So typically we look at something called white light, which are, you know, specific wavelengths of light without boring you about the details.
But there's a little bit of an extra in the red part that typically we as humans cannot perceive and see, yet it is actually used by bacteria to drive photosynthesis in these environments where We as humans cannot perceive light anymore, but they certainly can and they use it to survive.
So infrared light that this life is soaking up, turning into food for itself. It sounds almost science fiction. Tell me about how it works a little bit more technically.
Yeah, so, I mean, this is basically a discovery made 20, 25 years ago, which is a very special photopigment. So think chlorophyll, you know, what you also have in your average plant leaves that you look at when you look out the window. And this molecule has a slight modification to it and that actually allows it to harvest juice and
take in the light of this very specific wavelength, which is kind of so-called the red shifted. And so another one of these chlorophylls has been discovered in 2010. And so it really expands now the range of the ability to drive photosynthesis in different environments. And so that excited us quite a bit. And of course, the field overall.
Let's talk different environments, because if we zoom out and we think of what life needs to actually live, that sounds weird, but I guess it makes sense. We start to think out in the cosmos. What can we learn from the life that you've discovered about possible life out there far away around exotic stars on exotic rocks and things like this?
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Chapter 4: What is the significance of finding life in extreme environments?
Yeah, so I mean, I think astrobiologists are quite excited about this because it ultimately might give us some hinters and pointers where to look a bit closer. So I think, you know, many of the other kind of planets and stars that we can observe often are are exposed to quite a lot of UV light. You might have heard about that.
So you also get, as a human, if you're exposed to a lot of UV light, you get a sunburn. The same happens to bacteria. They ultimately can die if they're exposed to too much. And this is very, very hard radiation. So they basically die on the surface. So why not look below the surface, which obviously are caves? And so... Where do you do that? On Earth, in actual cave ecosystems on Earth.
So I think this is perhaps the closest analog, perhaps, we don't know, this is a hypothesis, to what might happen out in these other kind of planets that we have not yet discovered, but maybe where we should have a closer look about life.
If we go back to the caves, my understanding is the microbes you're discovering and studying that are absorbing this darkness, if that makes any sense, have been untouched for many millions of years, approximately 49 million years. It's kind of wild that these microbes have been isolated for that long, isn't it?
Yeah, I mean, I think we could define isolation, maybe human isolated. So probably there's a very low chance that humans have gathered down in these particular environments where we were. But I think there's a frequent exchange of bats, for example. Bats go in and out of these caves. So, I mean, there is life, of course, that also exchanges with the surface and the subsurface.
But as far as human interactions with some of these ecosystems, I think these are quite common. clean and extreme and really stable for what is available as kind of systems on planet Earth because we have basically polluted and touched most of these environments already as humans.
I personally have. I try not to though. Bad joke. What does that kind of isolation do to life as it evolves?
That is a good question, and I don't have an answer to it. I think evolutionary speaking, this is quite interesting. So what could happen when these microbes interact and what perhaps even novel molecules may you find down there that might help humans overall besides these photopigments?
Because I think there's a lot of interesting microbiology down there that is somewhat accessible, actually, yet quite hidden compared to, for example, marine ecosystems. So I don't have an answer to you, but I think those are the questions that I would love to delve a bit deeper into in my career now.
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Chapter 5: How does light play a role in photosynthesis in darkness?
Isn't that beautiful? So, I mean, I think this is really like, I mean, my career's choice as a microbial ecologist, this is what excites me. I think you can, anywhere you would look, you would most likely find life, even in the most extreme environments.
And so, you know, as you said, from the bottom of the ocean to, you know, our outer stratosphere, you will probably find some type of life signatures that really only underpins how important our planet ultimately is in this context.
Now, are there any other exciting facts or anything about this cave and the bacteria you found there that you want to share?
Yeah, so I think what I think really for me put it all together in an exciting story was that, you know, so yes, light goes down there. I think maybe that's exciting by itself and it's used. But I think what was really cool for me was that the internal cave environment, so the walls in a way, have probably a huge effect on that, what wavelengths are actually going into the bottom of the cave.
So think of it as like... Kind of a hall of mirrors, I think was mentioned in the article. So in a way that cave walls can reshape the light environment by themselves simply due to the material properties. And I think that's a super cool, both in terms of applied scientists, maybe we can use some of these materials to perhaps build systems that are more effective at
transmitting light, but also from a fundamental ecology standpoint that, you know, the environment ultimately sucks for these microbes. And I thought that was really, for me, tying it all beautiful together. So that was the most exciting finding for me besides, of course, finding these things down there. And what are the walls made out of? Limestone or something like that? Yes.
Yeah so they're limestone and so first tests that we did basically we showed that you know the internal reflectance as it is called in a way you know favors these infrared radiation that the red part of the light spectrum to go deeper down into the cave than the other ones and so there seems to be some kind of enrichment at the bottom of that due to the light reflective properties of the walls themselves.
Well, Lars Behrendt is a microbial ecologist at Uppsala University and the Technical University of Denmark. Lars, thanks for sharing your cave research with me. I really appreciate you coming on the show.
Thank you very much. I appreciate it. Thank you.
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