A bacterium discovered in a Californian lake appears to be able to
use arsenic in its molecular make-up instead of phosphorus – even
incorporating the toxic chemical into its DNA. That’s significant
because it goes against the general rule that all terrestrial life
depends on six elements: oxygen, hydrogen, carbon, nitrogen, sulphur
and phosphorus. These are needed to build DNA, proteins and fats and
are some of the biological signatures of life that scientists look for
on other planets.

Christened GFAJ-1, the microbe lends
weight to the notion held by some astrobiologists that there might be
“weird” forms of life on Earth, as yet undiscovered, that use elements
other than the basic six in their metabolism. —Guardian