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Many would have been disappointed by the much anticipated announcement by NASA of the discovery of a new kind of bacteria in Mono Lake, California. The reason is that what has been found is actually a microscopic organism belonging to the Gammaproteobacteria family, a common terrestrial life form.
However, this one is unusual, because in contrast to all other terrestrial life forms it can live on arsenic, not just for nutrition but also to build its own cellular structures.
The discovery was made by a group of researchers led by Felisa Wolfe-Simon, a NASA astrobiology research fellow working at the U.S. Geological Survey in Menlo Park, California.
It all started with some samples taken from Mono Lake (in the photo) which is known for its elevated salinity, alkalinity and high levels of arsenic, due to the fact that it has been isolated from fresh water sources for 50 years.
In these samples, researchers found a new bacterium, called GFAJ-1, that put in a culture demonstrated a taste for arsenic, to the point of being able to make do without phosphorous.
Phosphorous has always been thought to be fundamental for the development of any form of life because it forms part of the structure of DNA and RNA, along with carbon, nitrogen, oxygen, hydrogen and sulphur. Therefore, phosphorous is one of the six elements required in every terrestrial life form. At least until now.
Phosphorous is fundamental for cellular nutrition and the building of cellular membranes, while arsenic, although chemically similar to phosphorous, is poisonous for almost all living things, with the sole exception of a few microbes that can breathe it.
But evidently, as shown by the discovery of Wolfe-Simon and colleagues, there are life forms that live on arsenic, growing and reproducing, and if it happens on Earth (albeit in a restricted environment) it can happen elsewhere in the cosmos, on planets that have environmental conditions similar to those in Mono Lake.
It could have already happened on Mars, where the water dried slowly and would have undergone an increase in the concentration of salts, likely including arsenic. Future missions will now have to widen their search for signs of life to include those from life forms thought impossible up to now.
In general, the discovery of GFAJ-1 forces us to broaden our horizons as to what forms of extraterrestrial life may exist, and to re-think a great many established ideas in the fields of biochemistry and biology.
The results of the discovery have already appeared in Science Express and will shortly be published in the journal Science. |
