The bugs that came in from the cold
Locked in ice for millions of years, Antarctic bacteria are thawing - and they're alive. So will a prehistoric plague be swimming in a sea near you? Rob Sharp finds out
Published 26/09/2007 | 10:22
Antarctica's Dry Valleys are among the most desolate places on the planet. Here, no plants cling to the slopes, no small mammals scurry among the scree. The freeze-dried landscapes, with their rocks chiselled by the wind, seem utterly lifeless. When Captain Scott first chanced upon their craggy peaks and troughs in 1905, he labelled them the "valleys of the dead" .
Now, a little more than a hundred years on from Scott's exhibition, US scientists have discovered that the icy landscapes may not be so barren after all. Microbiologists from New Jersey have chanced upon tiny frozen organisms that have remained alive for millions of years, embedded in some of the oldest ice on the planet.
Dr Kay Bidle of Rutgers University, who was part of the research team, extracted DNA and bacteria from ice found barely metres beneath the surface of a Dry Valleys glacier, and, remarkably, claims to have grown the bacteria in a lab. "This is by far the oldest ice in which we have found encased microbes, cultured them and formed a growth," he says.
The discovery of such ancient viable genetic material has far-reaching implications, not least the possibility that global warming could melt Antarctic ice to such an extent that an army of invidious pathogens will be released to wreak havoc on humans. But a more realistic outcome is that the experiment will aid our understanding of evolution, and how life could survive on other planets. Not bad for organisms that are eight million years old, originating four million years before humans first got up and strolled about on two legs. "The study is interesting because it extends understanding of the period of time over which organisms remain viable," adds Dr Bidle, who published his research earlier this month.
Braving the barren hills, where footsteps made 50 years ago can still be seen, the researchers took samples that ranged in age from 100,000 to eight million years. Drilling deep beneath the shifting surface of an ice floe, they dredged up frozen material that, when scrutinised under a microscope, left them stunned. Not only could they see microscopic bacteria that they could extract, but these enduring creatures were from the most ancient ice samples.
Once the bacteria were extracted and fed in a laboratory, they began to multiply. While the number of organisms found in the 100,000-year-old ice doubled in size every seven days, those from the eight million-year-old ice grew much more slowly. Dr Bidle says that the "young stuff grew really fast", but the older colony doubled in size only every two months, suggesting that over time, the bacteria's DNA , which controls its reproduction, had been damaged.
The researchers claim this is the result of cosmic radiation - highly charged energy particles that whizz in from space and bash apart genetic material. This radiation is strongest at the poles, where the Earth's protective magnetic field is at its weakest. Comparing the genetic " mashing up" of the two samples, the scientists were able to calculate a half life for the bacterial DNA (how long it takes for half the DNA present in a sample to fall apart). The figure they came up with was a whopping 1.1 million years.
The scientific community has heralded the discovery as "significant" , but the team's conclusions might disappoint science-fiction buffs. There will be no global pandemic - or at least there shouldn't be. The scientists say that while extremely old bacteria will be released into the world's oceans as a result of global warming, it is not a "cause for concern" . Dr Bidle says that marine bacteria and viruses are less harmful to human health than those found on land. "Clearly this melting has happened many times over the Earth's history," he says. "We didn't find any pathogens. What we found were organisms closely related to common environmental bacteria."
The experts are keen to point out that even if ancient pathogens were released, they would not be very good at making people ill. In order to be effective they would have had to evolve in tandem with their original " target" - impossible for organisms that have been cut off for millenia.
Whenever the ice caps melt they inject a huge amount of genetic material into the oceans. Bacteria can incorporate external DNA into their own genetic material - through a process known as "lateral transmission" - and if they are good genes they can help the bugs survive. If they are not, they won't. "[Lateral transmission] can be advantageous or it can be deleterious. This is one of main ways in which microbes get new data," Bidle says. "It's up to natural selection to sort that out." In other words, the thawing of Antarctic ice could fast-track the microbes' evolution.
Moving back a notch, Bidle et al have shed light on how life on Earth began - or at least undermined a popular theory. Some scientists suggest a comet carrying the raw material for life crashed into the planet millions of years ago. But Bidle's team claim that, as the DNA in the old ice samples degraded massively as a result of exposure to cosmic radiation, life on Earth is unlikely to have come from outside the Solar System. A comet carrying life from beyond our immediate planetary neighbours would take so long to reach us that all the genetic material on it would be sterilised.
Study of the hyper-arid Dry Valleys can also further our understanding of conditions on Mars. Nasa scientists have long considered the valleys to be the most Mars-like environment on Earth. Mars has ice at both poles, and has geological features reminiscent of those found in Antarctica. Dr Bidle says: "If there are microbes stored here, then there could potentially be microbes stored in ice on Mars."
Not everyone has ratified Dr Bidle's research. Russell Vreeland of the Ancient Biomaterials Institute at West Chester University in Pennsylvania, heaped derision on the scientist's experimental methods. He said that the bacteria they "resuscitated" may be much younger than the team think, as it is extremely hard not to contaminate ice samples with unwanted microbes. "The procedures that were used were not the ones that I would have used," he says. "I they think they should have been more careful." However, the researchers claimed the type of growth they observed would not be seen with modern bacteria.
If their findings are true, Dr Bidle and his crack corp of marine experts will have considerably extended the record for the oldest DNA found frozen in ice. Earlier this year, a team of researchers from the University of Copenhagen announced they had recovered DNA from a Greenland ice sheet that was up to 800,000 years old. Dr Bidle seems to have smashed this record. " It's pretty significant in a number of ways," he concludes. "What we have here is something that significantly affects the tempo of microbial evolution on the planet." And much further beyond, we hope. Scott may have written in his Antarctic diaries: "Great God, this is an awful place." But it yields ceaseless wonders.
Life in the deep freeze
The most unusual fish in Antarctic waters, ice fish are the only vertebrates whose blood entirely lacks haemoglobin, the red oxygen-carrying pigment. As they have no haemoglobin, they have to compensate with other adaptations to low temperatures. They use less energy and have a larger heart, which pumps more blood around their bodies.
Less than 100 insect species have been recorded in Antarctica, and most of them are parasites, like lice that live in the feathers and fur of birds and seals. Springtails) are the only free-living insects. They feed on algae and fungi, and remain dormant in winter.
The omnivorous Odontaster validus, or red star, feeds on another sea star species, the larger Acodontaster conspicuus. Some starfish also congregate beneath seals' breathing holes, where they eat their faeces.
The wandering albatross flies thousands of kilometres around the continent in search of food, and is one of around 35 types of bird that comes to Antarctica. Others include gulls, cormorants and terns, which hunt closer inshore. Most return to the same sites each year.
The scyphomedusa, often seen in Antarctic waters, has tentacles that are over 9m long, and a body that can grow to over 1m in diameter.