NASA scientists found bacteria living in arsenic in a California lake
, a discovery that will impact the search for extraterrestrial life forms. The finding, presented by NASA
at a press conference today, was preceded by intense media speculation about the possibility that the U.S. agency would announce that it had found life in outer space.
The main factor that triggered the speculation was that NASA convened a press conference
to announce an “astrobiology finding that would impact the search for extraterrestrial life".
The discovery is expected to cause changes in the activity of NASA, which until now has sought life on planets which contained the elements that were thought could allow the development of living organisms.
The life forms known to date are mainly composed of six elements and compounds: carbon, hydrogen, nitrogen, oxygen, sulphur and phosphorus.
"Although these six elements make up nucleic acids, proteins and lipids and, therefore, the majority of living matter, it is theoretically possible that some other elements of the periodic table can perform the same functions,"
says Felisa Wolfe Simon
of the Astrobiology Institute at NASA's Menlo Park, California, which is published today in the Journal Science
The researchers found in the brackish, toxic waters of Mono Lake in California, a proteobacteria of the family Halomonadacea, strain GFAJ-1, that can completely replace phosphorous
with arsenic to the point of introducing this element into its DNA.
Arsenic is highly toxic to living organisms, at least those known so far, because it upsets metabolic processes, but chemically it behaves similarly to phosphate.
The space agency researchers cultured the bacteria, which grew and multiplied easily in the toxic environment in petri dishes in which phosphate salt was gradually replaced by arsenic. The process continued until the bacteria grew without phosphate, an essential element in the construction of several macromolecules present in all cells, including nucleic acids. The scientists used radioactive tracers to follow the path of arsenic in the bacteria, since ingestion of the chemical to its incorporation into various cellular components. They determined that arsenic completely replaced phosphorous in the DNA molecules of the bacterium.
"The switch of phosphorous to arsenic can have a profound impact and significance in biological and geochemical evolution."
the researchers conclude.