In an undated handout photo, Floyd Romesberg, a chemistry professor at the Scripps Research Institute and leader of a team that has created an organism with a partially artificial genetic code. The research, published on May 7, 2014, is likely to raise safety concerns and ethical questions, but scientists also say it could lead to medicines and industrial products that could not be made otherwise. (Scripps Research Institute via The New York Times)

The accomplishment might eventually lead to organisms that can make medicines or industrial products that cells with only the natural genetic code cannot. The scientists behind the work at the Scripps Research Institute have already formed a company to try to use the technique to develop new antibiotics, vaccines and other products, though a lot more work needs to be done before this is practical.

The work also gives some support to the concept that life can exist elsewhere in the universe using genetics different from those on Earth.

"This is the first time that you have had a living cell manage an alien genetic alphabet," said Steven A. Benner, a researcher in the field at the Foundation for Applied Molecular Evolution in Gainesville, Fla., who was not involved in the new work.

But the research, published online by the journal Nature, is bound to raise safety concerns and questions about whether humans are playing God. The new paper could intensify calls for greater regulation of the budding field known as synthetic biology, which involves the creation of biological systems intended for specific purposes.

"The arrival of this unprecedented 'alien' life form could in time have far-reaching ethical, legal and regulatory implications," Jim Thomas of the ETC Group, a Canadian advocacy organization, said in an email. "While synthetic biologists invent new ways to monkey with the fundamentals of life, governments haven't even been able to cobble together the basics of oversight, assessment or regulation for this surging field."

Despite the great diversity of life on Earth, all species, from simple bacteria to human beings, use the same genetic code. It consists of four chemical units in DNA, sometimes called nucleotides or bases, that are usually represented by the letters A, C, G and T. The sequence of these chemical units determines what proteins the cell makes. Those proteins in turn do most of the work in cells and are required for the structure, function and regulation of the body's tissues and organs.

The Scripps researchers chemically created two new nucleotides, which they called X and Y. They inserted an X-Y pair into the common bacterium E. coli. The bacteria were able to reproduce normally, though a bit more slowly than usual, replicating the X and Y along with the natural nucleotides.

In effect, the bacteria have a genetic code of six letters rather than four, perhaps allowing them to make novel proteins that could function in a completely different way from those created naturally.

"If you have a language that has a certain number of letters, you want to add letters so you can write more words and tell more stories," said Floyd E. Romesberg, a chemist at Scripps who led the work.

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Scientists Add Letters to DNA's Alphabet, Raising Hope and Fear