Some microbes can live for more than half a million years by repairing their DNA—so if Mars ever harbored similar life forms in its wetter past, they too might live on, scientists say.

Researchers announced the findings in this week’s early online issue of the research journal Proceedings of the National Academy of Sciences.

The findings might also apply to certain other Solar System bodies such as Jupiter’s moon Europa, they said. There, an icy shell covers what scientists think may be a liquid water ocean. Mars has very little known liquid water—essential to life as we know it—but it’s believed to have had much more long ago.


The Aureum Chaos region on Mars, in an image from the European Space Agency’s Mars Express spacecraft.

It’s also known that bacteria can survive for millennia, encapsulated in ice, sediments and other materials. But for how long they live has been unclear, as well as how they do it. The leading idea was that they go dormant to survive.

But such dormancy usually stops metabolism, including DNA repair. Without constant maintenance the genome is vulnerable to chemical reactions that damage the DNA. Eventually the genome accumulates so much damage that the cell can’t reproduce.

In the new work, Sarah Stewart Johnson at the Massachusetts Institute of Technology in Cambridge, Mass. and colleagues collected bacterial samples undisturbed for more than half a million years in the frozen grounds of Siberia and Canada.

They analyzed the DNA of the ancient cells, and also detected metabolic activity. The key to the longevity of these bacteria is continuous DNA repair, they wrote. They added that similar permafrost environments around the world may harbor species of viable bacteria adapted to past environments. An earlier study published in the journal’s Aug. 14 issue also proposed that as glaciers melt due to global warming, they might release ancient bacteria that become active again.


- Courtesy PNAS
and World Science staff

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