NASA Discovery May "Rewrite a Lot of Chemistry"
I never took Biology in school, and didn't really pay attention in Chemistry, but apparently one of the principles that has defined "life as we know it" is that phosphorous is a required chemical element, essential to the structure of DNA molecules. But today NASA scientists announced the results of a test demonstrating arsenic can be used in its place in some bacteria.

It turns out that that [Mono Lake], 13 miles east of Yosemite National Park, contains lots of arsenic as well as the usual phosphorus. Wolfe-Simon and her colleagues designed an experiment to take a particular type of salt-loving bacteria called GFAJ-1 from Mono Lake's mud sediments, wean it off phosphorus, and see if it could switch its diet to arsenic.

In the paper published today, the researchers report that some of the bacteria could survive on arsenic and incorporate it into their cellular biochemistry. Instead of the usual phosphate-rich DNA, they observed arsenate-rich DNA. Heightened levels of arsenic also showed up in the cell's proteins and fats. The scientists used mass spectroscopy, radioactive labeling and X-ray fluorescence to confirm that the arsenic was really being used in the biomolecules rather than merely contaminating the cells.

If that could happen in the laboratory, why couldn't it happen naturally? ASU astrobiologist Paul Davies, another one of the paper's co-authors, has long held that "weird life" -- based on chemical building blocks unlike our own -- could exist right under our noses on Earth, or in extraterrestrial environments.

Some scientists - particularly the ones who will have to rewrite the Chemistry books, I presume - are skeptical of these results, insisting that arsenic likely did not actually take the place of phosphorous, just became highly pronounced and accommodated by the bacteria in the experiment.