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Some New Life Form Lives On Arsenic

  • Bacterium in a lab thrived despite substituting one of the six building blocks of life.  
  • The finding has implications for the search for life beyond Earth -- as well as the prospect that alternative forms of life may exist on the home planet as well.
  • Scientists weaned a strain of bacteriaoff of phosphorus, leaving them to do-or-die with arsenic. Surprisingly, they lived.  
Strange bacteria living deep in a California lake can survive on arsenic and can even grow by incorporating the element into its DNA and cell membranes.

"It has solved the challenge of being alive in a very different way than we knew of," said lead researcher Felisa Wolfe-Simon, a biochemist with the U.S. Geological Survey in Menlo Park, Calif. 

GFAJ-1 is no Frankenstein monster. It's a bacterium scooped up from the salty sediments of Mono Lake in California that seems to have pulled off a major scrambling of its building blocks for life -- something scientists didn't think possible.

The finding not only presents the possibility that alternative life forms can exist, or once existed, on Earth. It opens the floodgates for scientists developing techniques to identify alien life, if it exists. And it raises the prospect of alternative methods for wastewater treatment and bio-energy production.

"The implications are profound, regardless. The building blocks of life are more flexible that we had previously thought," astrobiologist Ariel Anbar, with Arizona State University.

The life forms in question, GFAJ-1 of the Halomonadaceae family of Gamoproteobacteria -- like all living things -- were dependent on oxygen, carbon, hydrogen, nitrogen, phosphorus and sulfur to exist. But in the laboratory of Wolfe-Simon, a NASA astrobiology research fellow, the organisms learned to live with arsenic instead of phosphorus.

"Are the organisms actually doing this in Mono Lake, or do they have the latent ability to do so? That's an interesting question to pursue," said Anbar, a co-author of the study.

Analysis showed the transition was more than cosmetic. The microbes seem to have incorporated arsenic into their DNA. Wolfe-Simon accomplished this by not replenishing the phosphorus in their laboratory environment, forcing them to make do, or die, in a liquid that became increasingly more concentrated in arsenic, which from a molecular perspective, closely resembles phosphorus.

Surprisingly, the colony lived and grew.

"Nothing should have grown," Wolfe-Simon told reporters. "It was amazing. We have a microbe doing something different than life as we know it. We've cracked open the door to what's possible elsewhere in the universe."

Steven Benner, with the Foundation for Applied Molecular Evolution in Gainesville, Fla., would like to see more detailed studies on the chemistry, including radioactive tracers to map the location of arsenic in cells.

"Chemists think this is an exceptional result, and therefore chemists will, like Carl Sagan says, require exceptional evidence to prove it," Benner said.

If the study holds up, it could lead to a change in how phosphates are used and managed on Earth.

"Phosphate-based fertilizers are one of the pillars of the green revolution," said chemist James Elser, also with Arizona State. "They are limited in a lot of different ecosystems. Organisms rely on phosphorus to build nucleic acids and other molecules to grow and proliferate."

"Phosphorus is a big issue for sustainability and the quality of aquatic ecosystems. When it leaks out of systems, out of agricultural systems, it functions as a pollutant," Elser added. "It's really exciting to think about the possibilities that are raised by a clever organism that evolved a way to do without phosphorus, possibly... and how it might be used in wastewater treatment, recovering phosphorus from various sources, in bio-energy production."

The finding also will spur NASA to rethink how it goes about looking for life, particularly on Mars, the target for a new rover packed with biology and chemistry experiments that is due to be launched next year.

"It makes me have to expand my notion of what environmental constituents might enable habitability," said Pamela Conrad, a Mars Science Lab co-investigator with NASA's Goddard Space Flight Center in Greenbelt, Md.

"Perhaps arsenic is not an essential component for habitability or for life, but it may be one that can be tolerated," she added. "And that opens up our perspective to try to understand what other potential components might be tolerated, or in fact even essential, that we presently haven't thought of."

 by "environment clean generations"

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