Pond scum may hold tiniest known life-form

By William J. Broad
NEW YORK TIMES NEWS SERVICE

December 23, 2006

The smallest form of independent life known to science may have just gotten smaller.

Four million of a newly discovered microbe – assuming the discovery, reported yesterday in the journal Science is confirmed – could fit into the period at the end of this sentence.

Scientists found the microbes living in a remarkably inhospitable environment, drainage water as caustic as battery acid from a mine in Northern California.

The microbes, members of an ancient family of organisms known as archaea, formed a pink scum on green pools of hot mine water laden with toxic metals, including arsenic.

“It was amazing,” said Jillian F. Banfield of the University of California Berkeley, a member of the discovery team. “These were totally new.” In their paper, the scientists call the microbes “smaller than any other known cellular life-form.”

Scientists said the discovery could bear on estimates of the pervasiveness of exotic microbial life, which some experts suspect forms a hidden biosphere extending down miles whose total mass may exceed that of all surface life.

It may also influence the search for microscopic life-forms elsewhere in the solar system, a discovery that would prove life in the universe is not unique to Earth but an inherent property of matter.

The tiny microbes came from an abandoned mine at Iron Mountain in Shasta County, which produced gold, silver, iron and copper, and closed in 1963.

Today, rain and surface water run over exposed minerals, producing sulfuric acid. The mine is one of the largest Superfund cleanup sites.

Starting in 2002, the scientists obtained drops of the acidic slime and searched for genetic signs of novel microbes.

“We were essentially looking for new stuff,” said Brett J. Baker in a UC Berkeley statement, “and we found it.”

The microbes are about 200 nanometers wide.

That also is the size of large viruses. But most scientists do not consider viruses to be independent living organisms because they cannot reproduce on their own. Viruses hijack another organism's biological machinery to replicate.

Bacteria average about five times the size of the Shasta microbes.

The scientists must do further tests to confirm that the organisms are the smallest ever found, and that they can reproduce.

If those analyses hold up, they said in their Science paper, “it may be necessary to reconsider existing paradigms for the minimum requirements for life.”
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It's not that they don't consider viruses to be lifeforms, they merely don't consider them to be independent lifeforms, meaning that viruses could not be found to thrive on their own without the presence of other life. Scientists still consider viruses to be lifeforms.

That also is the size of large viruses. But most scientists do not consider viruses to be independent living organisms because they cannot reproduce on their own. Viruses hijack another organism's biological machinery to replicate.

This could be argued forever but hijacking and replicating sound very life-like to me. Viruses do things rocks can't do. Deliberately doing anything at all seems like a definition of life.