RANDOLPH E. SCHMID - The discovery of a strange bacteria that can use arsenic as one of its nutrients widens the scope for finding new forms of life on Earth and possibly beyond.While researchers discovered the unusual bacteria here on Earth, they say it shows that life has possibilities beyond the major elements that have been considered essential.
"This organism has dual capability. It can grow with either phosphorous or arsenic. That makes it very peculiar, though it falls short of being some form of truly 'alien' life," commented Paul C. W. Davies of Arizona State University, a co-author of the report appearing in Thursday's online edition of the journal Science.
Six major elements have long been considered essential for life – carbon, hydrogen, nitrogen, oxygen, phosphorus and sulfur.
But the researchers found that the bacteria, discovered in Mono Lake, Calif., is able to continue to grow after substituting arsenic for phosphorous. ...
The find is important in the search for life beyond Earth because researchers need to be able to recognize life, to know what life looks like, Anbar said. ...
Felisa Wolfe-Simon of NASA's Astrobiology Institute, who led the study, targeted Mono Lake because it has high arsenic levels.
Arsenic and phosphorous are chemically similar, so she speculated that a microbe exposed to both might be able to substitute one for the other.
"Arsenic is toxic mainly because its chemical behavior is so similar to that of phosphorus. As a result, organisms have a hard time telling these elements apart. But arsenic is different enough that it doesn't work as well as phosphorus, so it gets in there and sort of gums up the works of our biochemical machinery," explained Anbar.
The researchers collected the bacteria known as GFAJ-1 and exposed it to increasing concentrations of arsenic, which it was able to adapt to and grow.
The microbe does grow better on phosphorous, but showing that it can live with arsenic instead raises the possibility that a life form using arsenic could occur naturally, either elsewhere on Earth or on another planet or moon where arsenic is more common. ...
Further explanation of why this is so "alien".
All living organisms on this planet use six elements for almost all of the chemical structures of DNA, RNA, proteins, and lipids. There is a smattering of other elements, mostly metals, that are essential for biological functions (e.g., the iron in hemoglobin). However, we wouldn’t expect to find anything outside of carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus in the basic structures of biomolecules. Surprisingly, a team of scientists provide evidence in Science that another element, arsenic, can be incorporated into the basic chemical makeup of the macromolecules of life, replacing some of its phosphorus.
Evolutionary geochemist Felisa Wolfe-Simon, the lead author, and her colleagues found a strain of bacterium (GFAJ-1 of the Halomonadaceae family) that can grow in a medium abundant in arsenic and lacking phosphorus. The GFAJ-1 bacterium naturally resides in the arsenic-rich waters (200 uM) of Mono Lake located in California's Eastern Sierra, and it belongs to a family of proteobacteria that is known to accumulate arsenic. It's not remarkable that GFAJ-1 survives in high concentrations of arsenic, but what is startling is that it potentially integrates arsenic into its DNA and proteins. ...