Similar microbes discovered earlier were plagued by contamination controversy.
The
discovery of microbes in a subglacial lake on Antarctica (shown above
as a mosaic of satellite images) suggests that extraterrestrial life
might exist in places once thought uninhabitable.
Biologists have extracted mineral-eating microbes from a
lake buried a half mile below the surface of the West Antarctic Ice
Sheet, according to a new study published in Nature.
Earlier claims of similar microbes drawn from a different Antarctic lake,
say the study's authors, were controversial because the samples had
been contaminated—a problem eliminated in this case by especially
careful drilling techniques.
"The report is a landmark for the polar sciences," writes Martyn Tranter, a geochemist at the University of Bristol, England, who was not involved in the study, in a commentary also published in Nature.
It's also a landmark in the science of astrobiology, the search for life on other worlds. In recent years, scientists have come to understand that life can thrive in a much wider range of environments than they once believed, including superheated water at the bottom of the ocean and ice caves in Greenland. That suggests that extraterrestrial life might also exist in places once thought uninhabitable.
This
new identification of microbes in subglacial Lake Whillans, a
6-foot-deep, 20-square-mile (1.8 meters, 52 square kilometers) body of
water kept liquid by heat from the bedrock below and friction from
glaciers moving over that bedrock, just adds to the possibilities. The
authors' findings, Tranter writes, "beg the question of whether microbes
could eat rock beneath ice sheets on extraterrestrial bodies such as
Mars."
Antarctica Extremophiles
The
Lake Whillans microbes, which come from nearly 4,000 distinct species
or "operational taxonomic units" (groups of species with similar
characteristics), are chemoautotrophs,
meaning they get their energy not from sunlight nor from other
organisms that live on sunlight, but rather from minerals dissolved in
the water, including nitrites, iron, and sulfur compounds.
Given
their ability to exist without light or access to organic food sources,
the microbes could also be a model for life on Jupiter's ice-covered
moon Europa or Saturn's Enceladus. (See "The Hunt for Life Beyond Earth.")
To
prevent contamination of their samples, the scientists used hot water
to drill down through the ice—and although the heat alone would have
killed any bacteria that tried to hitch a ride down, the team took
additional precautions.
"We had a water purification system on site," said lead study author Brent Christner
of Louisiana State University, in Baton Rouge. "We used filters to
remove any particles down to the size of a bacterium, then blasted the
water with UV radiation, then heated it to 90°C [194°F]. What we were
drilling with was nearly pharmaceutical-grade water."
Signs of Life
The team pulled their samples from the lake early in 2013. At the time, John Priscu of Montana State University, in Bozeman, a co-author of the new paper and chief biologist of the Whillans Ice Stream Subglacial Access Research Drilling (WISSARD) program, told Nature that "Lake Whillans definitely harbors life."
But
it took more than a year of research to demonstrate "unequivocally"—as
Tranter puts it—that the microbes they found are truly native to the
lake.
"The details [of how this ecosystem operates] will be an important story to follow in the future," said Alison Murray, an expert in extremophiles at the Desert Research Institute in Reno, Nevada, who wasn't involved in this research.
The
scientists will return to Lake Whillans next January to take samples
from a different location, to see if they can find more, perhaps
different, organisms.
"What we've seen so far is very
novel," Christner said. "But that novelty comes largely from our own
ignorance." The more places biologists look for at least some type of
life, it seems, the more previously unsuspected species they seem to
find.
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