Million year-old microbes in ice

When bacteria or viruses become extinct this is usually a cause for celebration, but can we ever be sure that they are gone?
18 July 2014

Interview with 

John Priscu, Montana State University


When bacteria or viruses, like Smallpox, become extinct this is usually a cause for celebration, but can we ever be sure that they are gone? Entire communities of bacteria have recently been discovered to be hiding beneath antarctic ice from up to a million years ago. Chris Smith spoke to John Priscu of Montana State University who told him about how they found these microbial communities...

John - A few years ago, the deepest sample we drilled was 800 metres. It took about 3 days and we used a special drill that melted snow and then heated the snow up to about 95 degrees centigrade and shot it out a jet, we lowered that down through the ice and it made about a 50-cm diametre hole which stayed open about 2 days. So, we'd sampled around the clock to gather water underneath the ice sheet and bring it to the surface to do our experiment.

Chris - When something is 800 metres deep, how far back in time is that?

John - That ice near the bottom of the ice sheet can be up to a million years old. This is in Antarctica and about the oldest ice is about a million years old so it's some of the oldest and the most pristine water on our planet.

Chris - And you're specifically interested in what's living in that ice?

John - Exactly. Up until now, the Antarctic continent, it's been sort of depicted as a non-living part of our planet and one thing we're trying to do is change that conception. We're trying to show that there are ecosystems that exist in and underneath the ice.

Chris - These are microbiological communities, tiny microbes?

John - Exactly. Under the ice and in the ice, it's a pretty harsh environment. There's no solar energy to drive photosynthesis. So, there's really no plant-life down there. So, the organisms have to exist by obtaining energy. I always like to call it, "they're eating the rocks". So, they're actually mining the rocks for energy.  The temperatures down there, they're sub-zero. They're about minus 0.5 to minus 2 centigrade and they're under quite a bit of pressure. So, that's not really a good house to live in.

Chris - Are these organisms actually living or are they in a state of sort of suspended animation?

John - This is a question we've been addressing a long time. As we go down through the ice and take cores and look at the organisms in there, we can actually melt the ice and the organisms will come back to life. It's quite amazing. The oldest we've done it on is maybe half a million years and the organisms within a minute or 2 minutes are back doing metabolism. So, I think the organisms in the solid ice sheet are probably somewhat dormant. They're kind of organisms waiting for liquid water whereas when we go underneath the ice sheet and hit a liquid water pocket, those organisms do have the elixir of life, if you want it and that's liquid water. So, the work we recently did with sampling the water underneath the ice and we brought it to the surface, and those organisms were alive and living down beneath the ice sheet.

Chris - Tell us a bit about the organisms that you're discovering down there? What are they and why do they survive this incredible environment for potentially tens to hundreds of thousands of years?

John - These organisms are all single-celled bacteria. We see an ecosystem down there where organisms use minerals for the energy. We see another group of bacteria that actually can feed on them. That's what I mean by an ecosystem.  We're seeing organisms that complement each other here. These single-celled organisms are very good at being able to survive freezing and thawing. If I stuck my finger in a refrigerator and froze it and thawed a few times, that wouldn't be a good thing. It would all bleb up and turn black, and probably fall off. But a microorganism, you can freeze and thaw, and freeze and thaw a number of times, and they're good to go.

Chris - Do you think that they could be potential pathogens that are threats to humans locked away and when we melt the ice or if the ice is melted by global warming for example, that they could come out and could pose a threat?

John - We've clearly thought about the ramifications of these organisms being pathogens and released to the surface. So, to be pathogens of course, we have to have an immunity to these pathogens to survive. Now, if an organism has been out of contact with human population for a long time, humans can lose that immunity. So, we're going to have to look at the balance to see if the humans have lost our immunity to let's say, a smallpox well that would be a virus, but if we saw an anthrax bacterium in the ice or some other pathogenic organism, if we still retain the immunity to that organism, we should be okay. But if something comes out that we've lost immunity to, we would have to worry.

We thought about sending ice samples to the Centre for Disease Control and getting them screened, but we're looking at only a million years in history which is a pretty small window of evolution for organisms. The fact that we've now cultured a lot of these organisms and looked at their sequenced data, we're not seeing anything exactly really bizarre or any kind of really pathogenic strain. However, if we look at the ice sheet itself - now, I'm talking about what's at the bottom, but if we look at the ice sheet itself, we have an ice - sort of a history of our planet that goes back up to a million years. So, the material at the surface is young. As we get deeper, it gets older and older, and older. So, when we go back up to a million years and we're just starting to do this kind of science. But if we can sequence the DNA in these organisms, we may be able to trace anthrax epidemics and organisms that caused the plague in Europe, and things of that nature. We hope in the next 5 or 10 years to be able to do it as our sequencing methodologies get better and better.


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