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Arizona State University
Tempe, Arizona

Contact:
James Hathaway, jim.hathaway{at}asu.edu, (480) 965-6375 

February 14, 2003

Common desert organisms may help in search for life in space
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ASU geomicrobiologist Ferran Garcia-Pichel doesn't just study
microorganisms, he studies how they interact with and change their 
inanimate surroundings. In his work he searches for clues about the 
first type of organism to dominate the early earth continents -- clues 
he says lead him to believe their descendants, still standing in the 
deserts of the Southwest, could be similar to the last ones standing 
in the case of a drastic change.

Well, maybe not standing. These tough little critters, which thrive in 
desolate places and extreme conditions, have no legs.

They are the microscopic, single celled cyanobacteria -- one of the 
oldest life forms on Earth. While they may no longer dominate the 
planet, they are well known from their marine fossil stromatolites, 
and they still live with us here, forming soil crusts in the Arizona 
desert.

Along these lines, Garcia-Pichel and his collaborators will be 
presenting several papers and posters at the 2003 NASA Astrobiology 
Institute General Meeting at Arizona State University. These are on 
the topics of cyanobacterial community structure, microbial mats, 
desiccation under different conditions, molecular analysis of 
calcifying cyanobacteria, comparisons of rDNA sequences from
cyanobacteria, as well as the analysis of microbial nitrogen cycling 
in desert soil crusts.

The Earth is about 4 billion years old. Fossilized stromatolites 
(large deposits left by aquatic communities of cyanobacteria), the 
most common fossils from the Precambrian period, are known for about 
3.5 billion years.  That's more than 75% of the earth's history. The 
size and number of these fossils indicate that cyanobacteria once
formed the major ecosystems of the Earth. They were witness to nearly 
every stage in the earth's evolution.

Geochemical evidence shows that cyanobacteria also seem to have played 
a major role in transforming the early earth into the earth we know 
today. They invented oxygenic photosynthesis and through this turned 
the earth's biosphere from reducing to oxidizing.

Studying fossilized cyanobacteria allows us to study what life was 
like and how it evolved on what was in many ways a different planet. 
But there may be more to the story.  According to Garcia-Pichel, their 
role in the transformation of early life on land has not been duly
recognized, perhaps because terrestrial cyanobacteria do not fossilize 
as readily as their marine counterparts.

Scientists might have to look at indirect evidence -- a unique sort of 
chemical or mineral signature (known as a biosignature) that an 
organism leaves in its environment. The study of living cyanobacteria 
and the chemical biosignatures they leave in their environment is 
essential for the task of looking for past-life evidence on other 
planets and our own.

According to Garcia-Pichel, if we can learn how to recognize the 
signatures left behind by living terrestrial cyanobacteria on our 
planet today, we will soon be able to look for them in our geologic 
record, as well as on other planets. The key to finding their evidence 
is in figuring out their signatures.

Garcia-Pichel hypothesizes that, because they lacked competitors, the 
early earth's surface may at one time have been completely covered 
with cyanobacteria. But, as the diversity of life increased, things 
changed. The advent of plants with leaf-litter blocked much needed
sunlight from hitting cyanobacterial communities in the soil. In 
short, they were crowded out.

And this brings Garcia-Pichel and his colleagues to the deserts of the 
Southwest, where aridity limits plant development, soils are usually 
bare and cyanobacteria still thrive in communities known as soil 
crusts.

In some of the more pristine portions of the Arizona desert,
cyanobacteria essentially lead an existence of withstanding
desiccation and the insults of the environment, living one or two 
millimeters under the surface. From time to time, every monsoon or so, 
they get wet and come to the surface for a couple hours of activity. 
In these wet periods they multiply through cellular division and 
repair all the damage from the dry period.

During dry spells, the cyanobacteria (as well as other microbes that 
live within their community) just lay dormant and suffer what 
Garcia-Pichel calls "the slings and arrows of the Southwest." To 
minimize the effects of these slings and arrows, they secrete slime. 
This slime creates a crust that holds the soil of the cyanobacterial 
ecosystem in place. This slime essentially cements the desert crust
and stabilizes the soil, keeping it from blowing away in the wind.

Though cyanobacteria are too small to see with the naked eye, we 
definitely see their effects. Dust storms in the urban Arizona, as 
well as the unacceptably high particulate matter count, are enhanced 
by the loss of cyanobacterial soil communities from agriculture and
construction.

Garcia-Pichel and his colleagues plan to study modern desert soil 
crusts, a common and important remnant of cyanobacterial ecosystem, 
and how they undergo diagenesis -- the chemical transformations that 
occur after burial.

Cyanobacteria may be old, but the science and methodologies 
Garcia-Pichel and his colleagues incorporate in geomicrobiological 
research are new. According to Garcia-Pichel we are just beginning to 
understand how microbes can and probably do drive biogeochemical 
cycles.  "This area of geomicrobiology is really, in the Western
world, a novelty," says Garcia-Pichel, "people still are amazed that 
microbes can do things with minerals and rocks."

Novelty or not, Garcia-Pichel and his colleagues believe
geomicrobiology will help scientists understand the evolution of the 
earth, and the possible evolution of other planets in this solar 
system and beyond.

Speaking of the applications of their research to the question of 
Mars, Garcia-Pichel said, "If we postulate that water was not always 
relegated and then became relegated, and that microbial life was 
present, what kind of ecosystem would have been the last to be on the 
surface soils of Mars? It would have been something like desert crusts 
today. So just there our chances of finding some indirect evidence of 
life are highest, if we just know how to track, how to teat and how to 
recognize possible biosignatures from these ecosystems."

The NASA Astrobiology Institute is composed of over 700 researchers 
distributed at more that 130 research institutions across the United 
States. Its central offices are located at NASA Ames Research Center, 
in the heart of Silicon Valley, California. Additional information 
about the NAI can be found at its website:  http://nai.arc.nasa.gov

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