Organisms that carry the beefed-up DNA code could be designed to churn out new forms of drugs that otherwise could not be made, they have claimed.

"This has very important implications for our understanding of life," said Floyd Romesberg, whose team created the organism at the Scripps Research Institute in La Jolla, California. "For so long people have thought that DNA was the way it was because it had to be, that it was somehow the perfect molecule."

From the moment life gained a foothold on Earth the diversity of organisms has been written in a DNA code of four letters. The latest study moves life beyond G, T, C and A – the molecules or bases that pair up in the DNA helix – and introduces two new letters of life: X and Y.