The DNA of ancient microorganisms, long frozen in ice, may return to life with the melting of these ancient glaciers, a new study published online in this week's Proceedings of the National Academy of Sciences has revealed.
Until now, scientists didn't know whether such ancient, frozen organisms and their DNA could be revived at all or for how long the cells remained viable after remaining frozen.
As part of their study, lead author Kay Bidle, assistant professor of marine and coastal sciences at Rutgers, and his co-authors, Rutgers colleague Paul Falkowski, SangHoon Lee of Korea's Polar Research Institute and David Marchant of Boston University - melted five samples of ice ranging in age from 100,000 to 8 million years old.
"First, we asked, do we detect microorganisms at all; and then we did - more in the young ice than in the old. We tried to grow them in media, and the young stuff grew really fast. We recovered them [the microorganisms] easily; we could plate them and isolate colonies. They doubled every couple of days. By contrast, the microorganisms from the oldest ice samples grew very slowly, doubling only every 70 days," said Prof. Bidle.
The study further revealed that the DNA of the microorganisms in oldest ice showed an "exponential decline" after 1.1 million years, "thereby constraining the geological preservation of microbes in icy environments and the possible exchange of genetic material to the oceans".
"There is still DNA left after 1.1 million years. But 1.1 million years is the 'half-life' - that is, every 1.1 million years, the DNA gets chopped in half," said Prof. Bidle.
He said the average size of DNA in the old ice was 210 base pairs - that is, 210 units strung together. On the other hand, the average genome size of a bacterium is three million base pairs.
Prof. Bidle further said they chose Antarctic glaciers for their research because the Polar Regions are subject to more cosmic radiation than the rest of the planet and contain the oldest ice on the planet.