NASA life discovery:

New bacteria makes DNA with arsenic

Richard A Lovett

No, today’s NASA announcement is not about proof of life on another world.

A recent release hinting at ‘an astrobiology finding that will impact the search for evidence of extraterrestrial life’ had bloggers abuzz the past few days with speculation that the space agency had discovered extraterrestrial life.

The truth, however, is that scientists have found life on Earth that’s perhaps the most ‘alien’ organism yet seen.

A new species of bacteria found in California’s Mono Lake is the first known life-form that uses arsenic to make its DNA and proteins, scientists announced today.

Dubbed the GFAJ-1 strain, the bacteria can substitute arsenic for phosphorus, one of the six main ‘building blocks’ for most known life.

The other key ingredients for life are carbon, hydrogen, oxygen, nitrogen, and calcium.

Arsenic is toxic to most known organisms, in part because it can mimic the chemical properties of phosphorus, allowing the poison to disrupt cellular activity.

‘The newfound bacteria, described online this week in the journal Science, not only tolerates high concentrations of arsenic, it actually incorporates the chemical into its cells, the study authors found.

“It’s gone into all the vital bits and pieces,” BEYOND Center for Fundamental Concepts in Science at Arizona State University in Tempe Director study co-author Paul Davies said. While for now Earth is the only place we know that life exists, the discovery does hold implications for the search for life elsewhere in the universe, since it shows that organisms can exist in chemical environments biologists once wouldn’t have imagined.

Did life arise twice on Earth?

Astrobiologists found the arsenic-based bacteria while looking for a possible ‘second genesis’ of life on Earth. The scientists were hoping to find evidence of a ‘shadow biosphere,’ sometimes called Life 2.0. Such a discovery would prove that, before life as we know it came to dominate the globe, the world had actually seen a separate, independent origin of life.

“If life happened twice on one planet, it is sure to have happened on other planets around the universe,” Davies said.

Last year NASA’s Astrobiology Institute study leader Felisa Wolfe-Simon published a paper suggesting that one possible version of Life 2.0 would be a creature that chemically substitutes arsenic for phosphorus. So Wolfe-Simon and colleagues took samples of bacteria from California’s Mono Lake, a briny, arsenic-rich lake in a volcanic valley southeast of Yosemite National Park.

The scientists cultured Mono Lake bacteria in Petri dishes, gradually increasing the amount of arsenic while reducing phosphorus. Chemical analyses with radioactive tracers showed that the GFAJ-1 strain bacteria was in fact using arsenic in its metabolism.

“Most (organisms) die, but these live on,” study co-author Davies said.

Despite their oddity, however, the bacteria are genetically too similar to ordinary life to truly be descendents of a second genesis.

National Geographic News