Thursday, December 2, 2010

Subsisting on Arsenic, a Microbe May Redefine Life

Via (Science) -

Scientists said Thursday that they had trained a bacterium to eat and grow on a diet of arsenic, in place of phosphorus — one of six elements considered essential for life — opening up the possibility that organisms could exist elsewhere in the universe or even here on Earth using biochemical powers we have not yet dared to dream about.

The bacterium, scraped from the bottom of Mono Lake in California and grown for months in a lab mixture containing arsenic, gradually swapped out atoms of phosphorus in its little body for atoms of arsenic.

Scientists said the results, if confirmed, would expand the notion of what life could be and where it could be. “There is basic mystery, when you look at life,” said Dimitar Sasselov, an astronomer at the Harvard-Smithsonian Center for Astrophysics and director of an institute on the origins of life there, who was not involved in the work. “Nature only uses a restrictive set of molecules and chemical reactions out of many thousands available. This is our first glimmer that maybe there are other options.”


Four years ago, while studying at ASU, Wolfe-Simon proposed that some organisms in extreme environments might be adapted to use arsenic in place of phosphorus. Phosphorus is one of the elements essential to life's chemistry -- in addition to carbon, hydrogen, nitrogen, oxygen and sulfur. Arsenic, which is just below phosphorus on the periodic table, is poisonous precisely because it can take phosphorus' place in biomolecules.

"It gets in there and sort of gums up the works of our biochemical machinery," ASU's Ariel Anbar, a co-author of the Science paper, explained.


In the paper published today, the researchers report that some of the bacteria could survive on arsenic and incorporate it into their cellular biochemistry. Instead of the usual phosphate-rich DNA, they observed arsenate-rich DNA. Heightened levels of arsenic also showed up in the cell's proteins and fats. The scientists used mass spectroscopy, radioactive labeling and X-ray fluorescence to confirm that the arsenic was really being used in the biomolecules rather than merely contaminating the cells.

If that could happen in the laboratory, why couldn't it happen naturally? ASU astrobiologist Paul Davies, another one of the paper's co-authors, has long held that "weird life" -- based on chemical building blocks unlike our own -- could exist right under our noses on Earth, or in extraterrestrial environments.

"This organism has dual capability," Davies said in today's announcement. "It can grow with either phosphorus or arsenic. That makes it very peculiar, though it falls short of being some form of truly 'alien' life belonging to a different tree of life with a separate origin. However, GFAJ-1 may be a pointer to even weirder organisms. The holy grail would be a microbe that contained no phosphorus at all."

Davies said GFAJ-1 was "surely the tip of a big iceberg" -- and Wolfe-Simon agreed.

"If something here on Earth can do something so unexpected, what else can life do that we haven't seen yet?" she asked. "Now is the time to find out."

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