Unlocking A Frozen Lake's Bacterial Secrets
What does life truly need to survive? Writing in the Proceedings of the National Academy of Sciences, Alison Murray and colleagues describe a community of unusual bacteria that survive under 20 meters of ice in the dark, salty, sub-freezing waters of Lake Vida, Antarctica.
IRA FLATOW, HOST:
This is SCIENCE FRIDAY. I'm Ira Flatow.
FLORA LICHTMAN, BYLINE: And I'm Flora Lichtman. Up first, a new contender for biggest extremophile.
FLATOW: Extremophile, hmm.
LICHTMAN: Yeah, I don't know if that's a word.
FLATOW: Thirty years ago, when I visited - talk about extreme, I visited Antarctica, researchers were - actually I didn't go in there with them, but they were diving below the ice of one of the lakes there, it might have been Lake Vanda, I know I visited it, it's been a long time ago, to study the life under the ice, and that was really fascinating.
And it looks like they've continued to do that for at least three decades because this week, researchers described a community of bacteria that make their living frozen inside an Antarctic lake. It's super-salty, there's no sunlight. It's about negative 13 degrees Celsius, talk about extremophile, and their home is sealed off from the rest of the world for, oh, about 3,000 years.
LICHTMAN: That's so lonely. So what's life like for these Antarctic bacteria, and what can they tell us about the search for life on other planets? Joining us now to talk about that is Allison Murray. She's the co-author of a recent paper in the Proceedings of the National Academy of Sciences describing the research and an associate research professor in the Division of Earth and Ecosystem Sciences at the Desert Research Institute in Reno, Nevada. She joins us by phone. Welcome to the show.
ALLISON MURRAY: Hello.
LICHTMAN: Tell us what this environment is like where these guys were found.
MURRAY: Yeah, so the system is - the lake, as you said, is basically frozen, but at about 16 meters or 50 feet down under the ice surface, there is a matrix of brine that permeates through the ice, down to at least a depth of about 27 meters or 90 feet. And this brine is - the environment is dark. There's no solar energy getting down there. It's very stable. It's cold. The temperature is about minus 13.4, that's eight degrees Fahrenheit.
And it's able to stay liquid because of the high amounts of solutes in the brine, which keep it from freezing at that temperature. The geochemistry we characterized is very interesting and complex and is a very rich matrix of both salts, it's about six times as salty as seawater, has high concentrations of organic carbon and high gas concentrations of gases such as nitrous oxide and hydrogen.
LICHTMAN: So this is in the McMurdo Dry Valleys in Antarctica. And are the bacteria in these little salty rivulets in the ice, in these little channels?
MURRAY: Yeah, that's our best understanding right now is that the bacteria, that the brine is in fissures and in channels in the lake ice, and that is a pretty stable system, though probably dynamic to some degree, and under the lake ice cover.
LICHTMAN: What are they eating?
MURRAY: They are eating - this is a good question and a big part of our study. When we - we can tell that they are at least surviving, and they have low levels of metabolism, of protein biosynthesis. We think that they're eating probably a combination of the resources of the system. It's really quite energy-rich. There's a lot of carbon there. There are a lot of both oxidants and (unintelligible) in the system to provide energy.
There is no oxygen there, but there are a lot of other good substitutes for microbial metabolism. We think that they are probably eating and living off some of the resources that were buried in that ecosystem, the organic carbon resources that have been internally cycled since the system was isolated.
It's possible that they are also being fueled by some resources that are produced abiotically in the system, such as the molecular hydrogen that we detected, which we think is being produced by abiotic reactions between the brine and underlying sediments, some of which are - we encountered in the lower levels of the lake ice.
LICHTMAN: If they're sealed off, though, are they going to run out of food eventually?
MURRAY: Well, presumably that would be what we would think. We did some different types of back-of-the-envelope calculations to see what we could predict, and in some ways we would have predicted that the system would have already run out of energy.
The temperature is very limiting, though, here. At minus 13 and below degrees Celsius, we really don't know very much about the energetics of life at that level, and it looks like these cells are really more in a survival metabolism, maintenance metabolism than really growing and reproducing actively.
LICHTMAN: Give us the nitty-gritty on what these bacteria are. We love microbes, can't give us too much information on what they actually are. Do we - do they live in places that aren't as extreme?
MURRAY: Yeah, yeah, good question. So we characterized them in terms of their diversity based on the ribosomal RNA gene, and we can tell that they have organisms that fall into eight different phyla of bacteria. These - and we had detected at least 32 different species, and I'm sure that there's more the deeper that we look.
And the organisms are diverse in their physiological capability, if we compare them to cultivate representatives that have been isolated from other environments, mostly cold and salty environments in the Arctic and in Antarctica are kind of their nearest relatives in a lot of cases.
And they have a variety of metabolisms. So it looks like they're not all growing and making their living on way, that it's really kind of a diversity of ways that they could probably make a living in the system.
FLATOW: You know, this says to me, from the line in "Jurassic Park," life will find a way no matter what you throw at it. I mean, this kind of environment, and the bacteria live in there.
LICHTMAN: Yeah, I mean, are there places on Earth that are sterile?
MURRAY: Well, that's a good question. There are - you know, astrobiologists have been working in different environments, I think, and there is that question of whether there are places that are sterile, places where we thought, where there is no water has driven a lot of those questions. And so places like the Atacama Desert, where it rains, has in some places not on history.
But I think that - but even there they find that there are microbes in the soil crust. And good questions come from looking for life in the sub-glacial lakes of Antarctica and in Lake Vostok. And this year there's two other drilling projects that are going into different systems.
And so I think that for these really longtime isolated systems, it'll be really interesting to see what the results are there.
FLATOW: Well, thank you very much.
LICHTMAN: Thanks for joining us. Allison Murray is an associate research professor in the Division of Earth and Ecosystem Sciences at the Desert Research Institute in Reno, Nevada.
FLATOW: One more question before you go: Do you think there - this talks about how you might find life in other planets, perhaps, you know, the rings of - the moons of Jupiter, places where you don't - you know, it's pretty cold and frozen?
MURRAY: Yeah, I think that finding a system like this, it really is a new type of environment that we found here, and it's really expanded our vision of what is habitable and that if we look for some of the icy moons, right, of either Saturn or of Jupiter that this system may be one of the best analogs that we have right now on Earth for other systems like that, where we know that there are - there is ice and potentially similar habitats.
FLATOW: Sorry to interrupt, Flora. I had to get that...
LICHTMAN: No, I'm glad you got that question in there. It will recur later in the show. So good thing we covered it.
LICHTMAN: Thanks for joining us today, Allison.
MURRAY: OK, thank you very much.
LICHTMAN: Allison Murray is an associate research professor in the Division of Earth and Ecosystem Sciences at the Desert Research Institute. Transcript provided by NPR, Copyright NPR.