Researchers in California have for the first time created an organism whose genetic code comprises six letters instead of four. This means that the bacterium, described in a study published in Nature today, is the first life-form to contain artificial genetic building blocks.

When biologists talk about the letters in the DNA alphabet, they are actually talking about nucleotides: molecules that bind together to make up the DNA double helix. Normally, these molecules are made up of four letters: A,T, C, and G. But scientists at the Scripps Research Institute have managed to add a single pair of artificial "X" and "Y" nucleotides to the genetic code of an E. coli strain, reports The New York Times. And thus far, the bacteria appear to be reproducing normally and passing on the new X-Y pair to their offspring.

Floyd Romesberg, a chemist at Scripps who led the study, told the New York Times that adding letters to the genetic code will allow researchers to "write more words and tell more stories." But creating "new words" — new life-forms and never-before-seen proteins — is bound to ruffle a few feathers. Jim Thomas, a spokesperson for a Canadian advocacy organization called the ETC Group, told the New York Times that "the arrival of this unprecedented ‘alien' life form could in time have far-reaching ethical, legal, and regulatory implications."

For now, however, the researchers are still trying to figure out how long the bacteria can survive, and if it might be possible to produce a strain with more than one X-Y pair. In addition, the researchers haven't been able to show that the bacteria can use the DNA to produce novel proteins, so the experiment won't lead to new vaccines and drugs just yet. Finally, should the strain escape into the environment, it probably wouldn't survive for very long, Romesberg said, because it needs to feed on synthetic molecules to replicate — molecules that only the scientists can supply. This means that it could never infect other organisms in its current form, because it would most likely die. In fact, the only way it could survive "in the wild" is if it reverted back to the traditional four-letter DNA alphabet.