San
Diego, CA (6/24/98)- The discovery of bacteria growing in the one of
the coldest places on Earth could help in the search for life on other
planets.
A team of researchers discovered several new types of microorganisms
living below the surface of permanent ice layer in the Antarctic's
McMurdo Dry Valleys desert. They found communities of autotrophic cyanobacteria
as well as heterotrophic bacteria living in tiny pockets of liquid water
deep in the ice, all thriving at temperatures of -20 degrees C and below.
"This is a very barren environment with virtually nothing we usually
associate with living organisms. But these photosynthetic cyanobacteria
are alive, self-sufficient, and growing. They're able to live through the
harsh freeze-thaw cycle of the seasons, fix nitrogen and release oxygen
as they make carbohydrates from water and carbon dioxide. They have their
own little world there we knew nothing about," said Stephen Giovannoni,
associate professor of microbiology at Oregon State University.
The life forms survive with minimal nutrition, provided by light, water,
carbon dioxide, phosphate, nitrate and other minerals. These primitive
life forms survive under conditions that existed in the oxygen-rich atmosphere
of early Earth. The conditions also resemble those found on Mars and Jupiter's
moon Europa- two places where exobiologists say life could exist.
"It's been suggested that Mars is too dry and cold for life to exist.
But it's also known that both Mars and Europa have frozen water on or near
their surfaces. We speculate that in conditions similar to those we observed
in Antarctica, it would be a distinct possibility that similar life forms
exist on Mars or Europa, " said Giovannoni.
Tiny pebbles and grains of sand are a key element in the microenvironment
of these bacteria. These particles carry microorganisms and form a sediment
layer below the ice surface. These heat up on exposure to sunlight during
the Antarctic summer, creating small pockets of water. In the presence
of liquid water and carbon dioxide from the surface, the cyanobacteria
photosynthesize and produce organic carbon, which the bacteria use to make
carbon dioxide for the cyanobacteria, and the cycle repeats itself. This
microbial community also appears to generate an antifreeze-like substance
that keeps the water pockets liquid long enough for reproduction to take
place.
"We think we need to understand the interaction between organisms on
our own planet to give us some signs of what to look for in other systems. What we're saying is that for life
on the edge you need a consortium of organisms to exist," explained JohnPriscu,
a noted Antarctic research based at Montana State University-Bozeman.
The research suggests that even though the ambient temperatures on other
planets are quite low, soil particles could heat up enough locally through solar heating to support
formation of liquid water, microbial growth and reproduction, notes Dr. Hans Paerl, professor of marine sciences,
University of North Carolina at Chapel Hill: "Mars is a good example of
the kind of place where this might happen."
The research appears in the June 26,1998 issue of Science.
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