Researchers report in the journal Science the discovery of a bacteria in a mud sample from California's salty Mono Lake that is the first-known organism to use arsenic in its basic metabolism and genes.The finding would add deadly arsenic to the six basic elements believed needed for life — carbon, hydrogen, nitrogen, oxygen, sulfur and phosphorus. The six elements are such a fundamental tenet of biochemistry that finding a critter living on arsenic was a big surprise."It's doing something extraordinary," says team leader Felisa Wolfe-Simon of the NASA Astrobiology Institute in Menlo Park, Calif.
"This is an exceptional claim," said biochemist Steven Benner of the Foundation for Applied Molecular Evolution, in Gainesville, Fla. Though skeptical, Benner says if confirmed, the finding would suggest that life could function on other worlds, such as Saturn's frigid moon, Titan, where arsenic-based biochemistry could thrive."This is a transformational result for the field," says astronomer Dimitar Sasselov of the Harvard Origins of Life Initiative. "It goes back to the basic question of what is life, really?"
Astronomers have detected more than 500 planets orbiting nearby stars in the past two decades, raising expectations that future telescopes may peer at them for chemical signatures of life. If life can thrive on unexpected elements such as arsenic, Sasselov argues, the possibilities for alien life could widely expand.
Life on Earth depends on phosphorus as a key element in nutrients. The new bacteria, however, appears to partly swap out arsenic for phosphorus.In the study, the team grew generations of the bacteria in an arsenic-laced experiment, usually deadly to such microbes, and were surprised to see the bacteria thrive instead. "Life is extremely adaptable," says biochemist Jim Cleaves of the Carnegie Institute of Washington (D.C.). Yet, he's more skeptical that the arsenic finding could mean much about alien life. "We already knew bacteria in lakes live pretty close to the edge."NASA's announcement of a news conference that would "impact the search for evidence of extraterrestrial life," sparked a great deal of speculation. Mary Voytek, head of NASA's Astrobiology Program, said "I'm sorry if they are disappointed" for anyone expecting NASA to produce evidence of alien life.
