A video still collected by a remote-operated vehicle named Jason with the Woods Hole Oceanographic Institute in June 2022. Superheated water and nutrients from a hydrothermal vent off the Oregon coast support a wide variety of life.
Courtesy of ROV Jason/WHOI
Deep in the ocean, superheated seawater blasts out of cracks in the seafloor known as hydrothermal vents. Though they might sound inhospitable, these vents actually support a host of microbial life forms. New research from Portland State University shows just how diverse that life can be. Researchers identified thousands of microbes across 40 different vent populations, many of which have never been identified before. PSU biology professor Anna-Louise Reysenbach led the study and joins us with more details.
This transcript was created by a computer and edited by a volunteer.
Dave Miller: From the Gert Boyle studio at OPB, this is Think Out Loud. I’m Dave Miller. Deep under the ocean, superheated seawater blasts out of cracks in the sea floor. They’re known as hydrothermal vents. These vents actually support a wide variety of microbial life forms. New research from Portland State University shows just how diverse that life can be. Researchers found thousands of microbes across 40 different vent populations. Many of them had never been identified before. Anna-Louise Reysenbach led the study. She is a microbiology professor at PSU, and she joins us now with more details. Anna-Louise Reysenbach, welcome to the show.
Anna-Louise Reysenbach: Hey Dave, thank you very much for having me.
Miller: You’ve been to the bottom of the ocean. Can you give us a sense for what these hydrothermal vents look like?
Reysenbach: Well, it’s dark down there. As you start coming down, you start to see a little bit more life. You’ll see an occasional fish swim by. You start to see a few little white crabs. And then once you reach the bottom, you suddenly see this profusion of life, lots more life. Huge, big tube worms, these white worms with red plumes at the end. But you also see this smoky water, it looks like smoke coming out of these rocks which we call chimneys. And that turbulent smoky water is actually hydrothermal fluid, it’s the minerals precipitating out of solution as they mix with cold sea water. It’s this early life kind of experience.
Miller: How hot is the fluid that we’re talking about, the fluid that seeps down under the seafloor and interacts with the hot crust I guess, and then gets pushed back. What’s this fluid like?
Reysenbach: Originally it’s seawater, and then it percolates down through the earth’s crust, gets hot, reacts with rocks, gasses get added, minerals get added. And it gets really hot as it gets closer to the magma chamber and then gets forced back to the sea floor. That fluid can be over 300 degrees Celsius, which is about 500 Fahrenheit or more when it reaches the sea floor. So it’s very, very hot.
Miller: What does it take for life to survive down there? We’re talking, I imagine, about intense pressure just from the water above, all the minerals that super hot fluid has grabbed onto, plus the super hot temperature. What does it take for any kind of life to survive that?
Reysenbach: The microbes that are living there, they take advantage of the geochemistry in this hot fluid, and the thermal gradients. So as that hot fluid mixes with cold sea water, as I mentioned, the minerals precipitate out of solution, they make these minerals produce these porous rocks. And that’s a substrate for microbes to attach to. And then they are being bathed by all these chemicals that the microbes can use for their energy. And so they use geothermal energy, essentially, to live and thrive under these conditions.
Miller: You’ve been studying these microbes for a number of years now. What did you set out to do with your latest study?
Reysenbach: I guess I have to step back a little bit. When we study the microbial world, it’s really very different than the visual world, because microbes are not visible to the naked eye. And so when we try and study them, we have to try and either grow them in the lab and then identify them under the microscope, etc. But it’s really hard because when you look at it on the microscope, a microbe just looks like a blob. And so how do you identify one blob from another blob? So the technology over the last two decades has dramatically changed, where we can now go in and not try and grow the microbes anymore, but we actually go and extract the DNA of all the microbes in an environment. Then when we do that, once we have all the DNA, we can then get the DNA sequence of all of that DNA, all the different little organisms in the very mixed population of organisms in these communities. Once we have the genome sequence of that entire community of organisms, we can then reconstruct from that information; take the pieces of the puzzle, put the pieces of the puzzle together, and reconstruct individual genomes from that environment.
And just for the listeners, this is what we’ve been doing with the human microbiome as well.
Miller: To find out what lives inside us, and in some ways makes us who we are, the creatures that we symbiotically live with, or they live with us?
Reysenbach: Exactly! And we never knew that there were so many microbes associated with our bodies, that we are 90% microbial and the rest is our selves. So we’ve used that same technology that the human microbiome has used. We set out to do that at these deep sea vents to see how diverse are the organisms? What are we missing? Are there any new kinds of organisms that we’ve never previously discovered? Are there new branches of life?
Miller: And it seems that, and this isn’t a spoiler because I mentioned it in my intro, that the answers to those last questions were resounding yeses. Can you give us a sense for the numerical scale of the previously unidentified microbes that you and your team have now identified at these various vents?
Reysenbach: So just on this fairly limited study, about six or seven deep sea event environments around the world, we obtained over 3,600 genomes that we reassembled, like I just explained.
Miller: From individual species, 3,600 individual species of microbes of bacteria or other tiny organisms?
Reysenbach: Exactly. At least. And then of that group, we showed that 500 of those, 14% of those, were new genera. If you think about taxonomy, you have species, genus, family, order class, phylum, going down in order of specificity. In the Columbia Gorge, if you think of desert parsley, here’s a genus called lomatium oreganum, that’s the purple one. And then the yellow desert parsley is another species of lomatium. Well, we discovered 500 new genera. So whole new lomatium types, (but they’re not lomatium,) that had never been described, named, or anything. So that’s 14% of that.
I thought I’d provide a comparison of the microbiome, because recently there was a study that reported the microbiomes of people from 32 different countries, four different body sites, all over the world. Huge data set. In comparison, from that huge data set, 32 countries, they only found about two percent new species. Not genera, species. So really, if we try to see how many species we found, I can’t tell you because there were thousands from our vents.
Miller: How much do you know about what these organisms are? We’re talking about thousands, a nearly uncountable number of newly identified species. But what you have, if I’m not mistaken, is the genetic information, the code for these. How much do you know about what they actually do, what they eat, who eats them, who they want to infect?
Reysenbach: Exactly. So that’s what you can do with those genomes, you can figure out what are they doing? What do they eat?
A lot of them are sulfur metabolism, because there’s lots of sulfide and sulfur minerals in these systems. A lot of them are using carbon dioxide, like plants, they will fix carbon dioxide and convert it into organic carbon.
Miller: But not using sunlight, right? Because there’s no sunlight way down there.
Reysenbach: Correct. And so those are called chemolithoautotrophs, instead of photoautotrophs. There’s a lot of those kinds of organisms.
But the other really interesting thing is from these genomes is some of the genomes are very reduced. So they can’t make everything, they can’t make their own energy, for example, some of these organisms. And so they have to rely and cross feed, they have to share food with other organisms or get energy from other organisms. And we’re able to see that by studying the actual genomes that we’ve retrieved. There are quite a few groups, clades of organisms, that we can now say for sure they cannot live alone, they need another partner to be able to survive in these conditions.
Miller: By virtue of the relatively limited number of genes, you know that they have to live in concert with other species?
Reysenbach: Exactly. Really cool.
Miller: A few years ago a release from British researchers said that their work “added to evidence that the origin of life could have been in deep sea hydrothermal vents rather than shallow pools.” Is that a mainstream theory? Do scientists like you believe that some version of the life that you’re just starting to learn more about way at the bottom of the ocean, that that was the beginning of life on Earth?
Reysenbach: Whether it was a warm pool or hot pool, I think is debatable. But definitely high temperatures, because early Earth was extremely volcanically active. There was so much bombardment from meteorites. It is thought that when life originated on this planet, where life was protected would actually be down deep in the ocean at some of these deep sea vents. And so this is where they could have survived through all that very volcanically and meteorically active early Earth.
Miller: We’re talking about a really hot, high pressure, mineral laden habitat. Is it possible to recreate that in a lab, and to actually grow the species that you’re most interested in, so you can actually watch them in action?
Reysenbach: My lab has done quite a lot of growing some of the organisms that we find in these genomic sequences. We’ve been able to grow them in the lab under limited pressure, not very high pressure. But we recreate some of the minerals that they need and figure out what energy and what carbon sources they need. And we’ve been quite successful at being able to grow some of these new genera that I just described.
But there’s also other people that actually study them under the very high pressures that these organisms exist, and they’re also successful at doing that.
Miller: What are you most excited to investigate next?
Reysenbach: Well, I’m really interested to know, is this just a study of 40 environments? And so if I look further, will I start to see just the same things? Or are we gonna see some different lineages of life? I’m really interested in knowing how the subsurface geology below these hydrothermal vents actually affect the kinds of microbes that are able to colonize and adapt to these systems. I would like to go to some of the other environments that we’ve been to and do the exact same study to actually begin to predict, based on the geochemistry and the geology of the environment, what we would find in terms of the microbes.
And then also using the genomes, I’d like to try and grow some of the ones that we’ve now discovered that are really unusual and novel, one especially the ones that need other things to grow with.
Miller: What do you think these deep sea microbes can tell us about life on the surface?
Reysenbach: That’s an interesting question. Well, it tells us that we’ve still only started to scratch our understanding of microbial life on this planet. And that they’re a huge genetic resource for many other kinds of novel discoveries. And there may be life elsewhere in the solar system that is very similar to the organisms that we study here.
Miller: Not just at the surface, but well above our surface. Anna-Louise Reysenbach, thanks very much for joining us.
Reysenbach: Thank you very much. That was fun.
Miller: Likewise. Anna-Louise Reysenbach is a professor of microbiology at Portland State University. She joined us to talk about her team’s recent work showing an even larger profusion of life at a super heated vent at the bottom of the ocean than was previously thought.
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