[meteorite-list] Scientists Say 'Nannoballs' Could Be Tiniest Life Form

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:34 2004
Message-ID: <200308201703.KAA04618_at_zagami.jpl.nasa.gov>

http://www.centredaily.com/mld/centredaily/news/6562301.htm

Scientists say `nannoballs' could be tiniest life form
BY ALEXANDRA WITZE
The Dallas Morning News
August 18, 2003

(KRT) - Nannobacteria could be the smallest living things on Earth, a Lilliputian
oddity worthy of listing in the Guinness Book of World Records.

Or they could just be figments of a powerful imagination combined with a powerful
microscope.

New experiments, done in Arlington, Texas, could help scientists decide between
these options. Two researchers have struck the middle ground by suggesting that
nannobacteria aren't living things - just the decayed leftovers of previously living
things.

The work has implications on Earth as well as other planets. If nannobacteria are
real, they would redefine the lowest size limit that life can attain. They might even
prove to be the first extraterrestrial life discovered; in 1996, NASA researchers
announced that tiny wormlike shapes in a Martian meteorite were proof of fossilized
Martian life, a claim now dismissed by most other scientists.

"It would be worth the price if someone could prove these are tiny life forms," says
Jurgen Schieber, a geologist at Indiana University in Bloomington who did the
experiments while at the University of Texas at Arlington.

Nannobacteria appeared on the scientific radar screen in the early 1990s, when
geologist Robert Folk identified structures that looked like bacteria in rocks from
central Italy. The problem was, the structures were just 50 to 250 nanometers, or
millionths of a millimeter, across - and the smallest acceptable size for living things
was supposed to be at least 200 nanometers. Cells just shouldn't be able to operate
if they were any smaller than that, scientists thought.

Dr. Folk called the tiny structures "nannobacteria," using a recently coined term that
adopted the paleontological tradition of spelling the prefix with two N's. He then
embarked on a decade of trying to photograph the structures in lots of different
geological settings.

"We're discovering new things because this is a world nobody's bothered to look at
at high magnification," says Dr. Folk, a professor emeritus at the University of Texas
at Austin.

But few biologists have joined his quest.

A 1998 analysis by the National Academy of Sciences, prompted by the excitement
over the Martian meteorite, reiterated that the smallest possible size for cellular life
was 200 to 300 nanometers across.

And then Dr. Schieber entered the fray, just by joking around with a colleague at the
microscope one afternoon.

He and Howard Arnott, a UTA biologist, were looking for pyrite, or fool's gold,
synthesized by microorganisms teeming in wet sediments.

They buried a piece of squid tissue in watery mud and let the microbes work.

But under the microscope, at scales much smaller than the expected microorganisms,
the scientists saw blobby shapes pop into view.

"When we cranked up the magnification we saw tiny little balls," Dr. Schieber
remembers. "I said, Look, Howard, these are nannobacteria. And he's a biologist, so
he took that as a joke."

But after staring at enough "nannoballs" through the microscope, the two became
intrigued enough to run some experiments.

In a tank they buried small pieces of bacteria-laced squid (to represent marine
tissue), beef (because its muscle fibers are well-understood) and pinto beans (for
vegetable matter). The scientists pulled tissue out of the muck every few days and
studied it for evidence of nannobacteria.

And they found, says Dr. Schieber, that "as long as there was stuff to decay, there
were nannoballs."

In the August issue of Geology, the scientists argue that structures called
"nannobacteria" may be just natural byproducts of tissue decay. If so, nannobacteria
wouldn't represent living organisms. But they could serve as a proxy, indicating that
normal-sized microbes had been at work there.

There's one major hitch to the UTA work: It applies only to sedimentary rocks, those
laid down by wind and water.

The work can't explain nannobacteria-like features found in volcanic rocks or
meteorites, for example.

Dr. Schieber, who studies the interaction of bacteria and rocks, says
nannobacteria-looking things appear frequently in sedimentary rocks.

"I just wanted to provide a more plausible explanation for why they are there," he
says.

Dr. Folk says the new study is a welcome addition to the scanty scientific literature
on nannobacteria.

"It's a good explanation for some examples (of nannobacteria), but it certainly is not
a worldwide explanation for all examples," he says. "If they were right, this would
mean that on Mars we have advanced vegetables who die."

Other researchers have proposed similar theories before, notes Kenneth Nealson, a
geobiologist at the University of Southern California. In 2001, a team led by
Hojatollah Vali of McGill University suggested that proteins could serve as
biological seeds around which minerals could precipitate, thus creating
nannobacteria-like structures.

The UTA work, says Dr. Nealson, is along the same lines.

"I think these guys have the right idea," he says, "although I doubt that they can say
that all nannobacteria are due to things like this, any more than Bob Folk can say
they are all nannobacteria."
Received on Wed 20 Aug 2003 01:03:20 PM PDT