Multitude of microbes thrives in the icy waters
In January 2013, researchers pulled the first water samples from a dark, frigid lake sealed beneath the Antarctic ice sheet. Within hours, they announced they had found live cells in the water (SN: 3/9/13, p. 12). Now after remaining tightlipped for 19 months, the team reports in the Aug. 21 Nature that the lake doesn't just contain microbial life, it teems with it.
“The number of microorganisms we saw in the water was very comparable with what you’d find in a typical surface lake or in the ocean,” says microbiologist and lead author Brent Christner of Louisiana State University in Baton Rouge. “We were very surprised.”
Christner’s team had used hot water to carefully tunnel hundreds of meters down, through the West Antarctic ice sheet to breach the surface of Lake Whillans. The surprising abundance of bacteria and single-celled organisms called archaea in the lightless lake, roughly 130,000 cells per thimbleful, ends a decades-long hunt for evidence of life wedged under the Antarctic ice.
Rivers and more than 400 subglacial lakes kept liquid by geothermal warmth crisscross the land beneath Antarctica’s 14-million-square-kilometer ice sheet. In 1999 researchers announced that ice cores collected above Lake Vostok in East Antarctica contained the first evidence of life in a subglacial lake.
Critics, however, suggested that the scarce dead cells in those cores were contamination from the drilling process. Since then, research teams from Russia, the United Kingdom and the United States have drilled into the ice in hopes of finding definitive proof of life.
In their work at Lake Whillans, Christner and colleagues fabricated a new type of drilling rig to minimize potential contamination. Before drilling begins, the rig heats filtered water, scorching any microbes. The water is then further disinfected with hydrogen peroxide before getting zapped with intense ultraviolet to kill off any remaining microorganisms. The rig pumps the thoroughly treated water down what Christner describes as a kilometer-long industrial garden hose, melting a 60-centimeter-wide cylindrical hole in the ice.
The precautions aren’t just for getting a definitive scientific result, Christner says. “The last legacy that we’d want to leave is messing up the lake with foreign material that might alter it.”
In January 2013 the team quickly and carefully drilled 800 meters into the West Antarctic ice sheet, penetrating the lake’s surface (SN Online: 1/28/13). Lowering sterilized equipment including a camera into the hole, the researchers retrieved 30 liters of lake water along with sediment cores from the lakebed. Christner says the amount of life in the samples was staggering: The researchers found genetic traces of 3,931 microbial species or groups of species.
Unlike life on the surface, Lake Whillans’ microbial inhabitants live a pitch-black existence. Without sunlight for photosynthesis, many of the microbes eat away at the lakebed’s rock and produce energy by oxidizing iron. These specialized microbes become food for other bacteria and archaea in the lake, the team surmises.
“It was more beautiful than I could have imagined,” he says. “We found all the elements for there to be a sustained ecosystem. It’s perfect.”
Christner suggests that the vibrant ecosystem fueled by these rock-chomping microbes supports the idea that life exists elsewhere in the solar system, such as under Mars’ polar ice caps or in a subsurface ocean on Jupiter’s frozen moon Europa (SN: 5/17/14, p. 20).
Biogeochemist Martyn Tranter ofthe University of Bristol in England agrees. “It’s not too much of a stretch of the imagination,” he says, to now think “that ice sheet beds on other planets and terrestrial bodies can be hosts to microbial life.”
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