Discovery of arsenic-based life form stuns scientists

The discovery of bacteria that can substitute arsenic for phosphorus at the DNA level has led to suggestions of a "shadow biosphere" on Earth.

A team of US researchers working on samples drawn from California's Mono Lake found what is believed to be the first living organism to exist without phosphorus in its DNA structure.

Instead of the substance, which was previously thought to be one of the six elements essential for life, the bacteria uses the deadly poison arsenic as one of its chemical building blocks.

Dr Felisa Wolfe-Simon, lead author of the study and a member of NASA's Astrobiology Institute and the US Geological Survey in Menlo Park, described the findings as "a reminder that life as we know it could be much more flexible than we generally assume or can imagine".

The bacteria violate a universally accepted rule of biochemistry that states all life on Earth must be built around the elements of carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur.