Upper Victoria Glacier, Victoria Valley, McMurdo Dry Valleys, Antarctica. Credit: David Saul.
Researchers have for the first time sequenced the genomes of ‘endolithic’ bacterial communities, that dwell inside porous rocks and are able to resist the hostile conditions found in the Antarctic desert. By analysing the genomes, they concluded that those bacteria had likely adapted to frost hundreds million years before Antarctica became what it is now.
In an expedition funded by the Italian National Program for Antarctic Research (PNRA), biologist, Laura Selbmann, from Università della Tuscia lived for more than a month in a tent in the middle of McMurdo Dry Valleys, a rocky desert in Antarctica that was once covered in ice and is now one of the driest environments on Earth. “In the hottest days the temperature was -25°C,” she explains. “Sometimes the wind froze specimens’ plastic bags causing them to shatter in my hands like crystal.”
In the end, Selbmann and her colleagues managed to collect several rock samples from rock at various altitudes and with various sun exposure. Using bioinformatics, 497 draft bacterial genome sequences were assembled, and clustered into 269 candidate species. “Most of these candidate species are totally unknown and absent from existing databases” explains Omar Rota-Stabelli from the Università di Trento, a co-author of the study1 published in Microbiome.
A technique called molecular clock allowed to determine that the majority of these new species diverged from known, related species about 1 billion years ago. “At first, I was shocked,” continues Rota-Stabelli. “I assumed there was a mistake”.
That date is so surprising because, up to 25 million years ago, Antarctica was part of the supercontinent Rodinia, that also included parts of today’s North America, West Africa, Europe and Australia. This means that the evolution of these extremely ancient bacteria has nothing to do with the recent geological history of the continent. Rather, they are probably remnants of ancient bacterial groups that, during the Tonian glaciation (about 1 billion years ago) diversified from pre-existing species by adapting to frost. These species then spread further in Antarctica once the present climatic conditions were established.
The study also gives insights in astrobiology. The McMurdo Valley is the terrestrial environment most similar to Mars, and if life ever evolved there it may have avoided extinction by staying inside rocks just like these Antarctic bacteria.
