The halophile Halomonas sp.

In 2010 a bacterium (Halomonas sp. GFAJ-1) was found by a researcher at a really salty lake in California called Mono Lake. The organism was profoundly unique in that it appeared to use arsenic instead of phosphorous in its DNA backbone (http://www.ncbi.nlm.nih.gov/pubmed/21127214?dopt=Abstract&holding=npg).

single strand of DNA, sugar phosphate backbone and nitrogenous bases

It's difficult to appreciate how impossible that discovery was without knowing that arsenic is poisonous to all life for it's very deadly propensity of replacing the phosphorous group in the DNA backbone (usually phosphate groups bond to the different deoxyribose groups of neighboring nucleotide monomers) and reaping total chaos in normal organisms.

This organism was not only living in a high arsenic environment and somehow tolerating what few other life form can tolerate, it was also incorporating the arsenic into its DNA and using it to replace the phosphorous with arsenic! And surviving generation after generation.

Halomonas sp. GFAJ-1 grown on arsenic 
(credit: Jodi Switzer Blum) http://www.nasa.gov/

 


Totally crazy.

Turns out it doesn't seem to be supported by further testing. The 2010 data supported the hypothesis that the bacterium was replacing phosphorous in its DNA for arsenic. However, more detailed testing revealed this not to be the case: http://www.sciencemag.org/content/337/6093/467.abstract

The evidence of arsenic bonding seems to more likely be abiotic and an explanation for the misleading data collected by the earlier researcher.

So no entirely new life form, however, a perfect example of a halophile (high salt environment loving bacterium) and a wonderful chance to see science at work on a cool subject.