SCIENCE -- December 2, 2010 at 4:44 PM ET
Arsenic and Old Space Thinking: NASA Discovery Spurs New Ideas on Life
Scientists found the microbe in California's Mono Lake (Photo Credit:Science/Henry Bortman)
A newly discovered microbe that can survive on arsenic rather than phosphorus could change the way scientists think about life on earth and search for life on other planets, NASA announced Thursday.
For years, scientists have believed that phosphorus is one of six essential elements that all living organisms need to survive -- the others are hydrogen, oxygen, carbon, nitrogen and sulphur. But the bacteria that researchers Felisa Wolfe-Simon and her colleagues found in California's arsenic-heavy Mono Lake seem to be able to replace phosphorus with arsenic at the most basic cellular level.
"It has solved the challenge of being alive in a very different way than we knew of before," Wolfe-Simon says. The discovery opens the possibility that astrobiologists searching for life on other planets could look for it in places, and in forms, that they never would have thought possible. The study was released Thursday by the journal Science.
Arsenic is just one step below phosphorus on the periodic table, and behaves in many similar ways -- that's what gave Wolfe-Simon and her colleagues the idea that there might be some life forms that could swap the two. To test that idea, they gathered microbes from Mono Lake, which has extremely high arsenic levels. Then, they grew the microbes in a lake-like solution, but gradually swapped out the phosphorous in the solution with arsenic. They found that one type of bacteria, GFAJ-1, continued to grow more strongly than the others.
When they tested a batch of the bacteria grown with only arsenic, they found that arsenic was present inside the cells in amounts that suggested that the bacteria were using arsenic in ways they would normally use phosphorus -- including as the backbone of their DNA.
"This is a phenomenal finding. We are talking about taking the fundamental building blocks of life, and replacing one of them with [...] another compound," Mary Voytek, director of NASA's Astrobiology Program, said in a news conference. She said that the discovery points to one of the greatest challenges about searching for extraterrestrial life: "Clearly if we went to another planet and saw a human, we would recognize it as life. The challenge of finding something that is really different is what plagues us."
Some researchers took the results with more caution. Steven Benner, a chemist at the Foundation for Applied Molecular Evolution in Gainesville, Fla., said that the results are intriguing but that more work needs to be done to prove definitively that the bacteria have really replaced phosphorus with arsenic in their DNA -- and are not just using the arsenic in other, less fundamental, ways.