A hardy bacteria common
on Earth was surprisingly adaptive to Mars-like low pressure, cold and carbon
dioxide-rich atmosphere, a finding that has implications in the search for
extraterrestrial life.
The bacteria, known as Serratia
liquefaciens,
is found in human skin, hair and lungs, as well as in fish, aquatic systems,
plant leaves and roots.
"It's present in a
wide range of medium-temperature ecological niches," microbiologist Andrew
Schuerger, with the University of Florida, told Reuters.
Serratia
liquefaciens
most likely evolved at sea level, so it was surprising to find it could grow in
an experiment chamber that reduced pressure down to a Mars-like 7 millibars,
Schuerger said.
Sea-level atmospheric
pressure on Earth is about 1,000 millibars or 1 bar.
"It was a really
big surprise," Schuerger said. "We had no reason to believe it was
going to be able to grow at 7 millibars. It was just included in the study
because we had cultures easily on hand and these species have been recovered
from spacecraft."
Contamination
Risk
In addition to concerns
that hitchhiking microbes could inadvertently contaminate Mars, the study opens
the door to a wider variety of life forms with the potential to evolve
indigenously.
To survive, however,
the microbes would need to be shielded from the harsh ultraviolet radiation
that continually blasts the surface of Mars, as well as have access to a source
of water, organic carbon and nitrogen.
NASA's Curiosity Mars rover is five
months into a planned two-year mission to look for chemistry and environmental
conditions that could have supported and preserved microbial life.
Scientists do not
expect to find life at the rover's landing site - a very dry, ancient impact
basin called Gale Crater located near the Martian equator. They are however
hoping to learn if the planet most like Earth in the solar system has or ever
had the ingredients for life by chemically analyzing rocks and soil in
layers of sediment rising from the crater's floor.
So far, efforts to find
Earth microbes that could live in the harsh conditions of Mars have primarily
focused on so-called extremophiles which are found only in extreme cold, dry or
acidic environments on Earth.
Two extremophiles
tested along with the Serratia liquefaciens and 23 other common
microbes did not survive the experiment, which not only replicated Mars' low
pressure, but also its cold temperature and carbon dioxide-rich atmosphere.
Follow-up
Studies
A follow-up experiment
on about 10,000 other microbes retrieved from boring 40 to 70 feet (12 to 21
meters) into the Siberian permafrost found six species - all members of the
genus Carnobacterium - that could survive and grow in the simulated Mars
chamber, located at the Space Life Sciences Laboratory adjacent to NASA's
Kennedy Space Center in Florida.
The next step is to see
how the microbes fare under even more hostile conditions, such as higher salt
levels, more radiation and less water.
Related studies to
analyze the genetics and metabolism of the common bacteria Serratia
liquefaciens
also are under way.
"In the search for
life on another planet, we have to start with something that we at least have
access to. We don't have a Martian bacterium we can experiment with, not yet,
so we keep trying to see if some of our own hardy micro-organisms have the
ability to grow at another location," Schuerger said.
"If we can never find
a microbe that can grow under conditions on another planet, then it starts
implying that life may not exist on that other location," he said.
The studies appear in
the Dec. 19 edition of the Proceedings of the National
Academy of Sciences and
this week in the journal Astrobiology.
Sources :
http://www.voanews.com/content/hardy-earth-microbes-may-resist-conditions-on-mars-reuters/1580841.html
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