Professor Floyd Romesberg (right) and Graduate Student Yorke Zhang led the new study at The Scripps Research Institute, along with Brian Lamb (not pictured). (Photo Credit/The Scripps Research Institute, Madeline McCurry-Schmidt)

WASHINGTON, Jan. 23 (Xinhua) -- U.S. scientists on Monday announced the development of the "first" stable semisynthetic organism, an advancement that may have major implications for medicine and even pave the way for the creation of new life forms.

"We've made this semisynthetic organism more life-like," senior author Floyd Romesberg, professor of the Scripps Research Institute, said in a statement.

The DNA of all life on Earth is built from four natural bases, called A, T, C and G, but in 2014, Romesberg and colleagues expanded life's genetic code from four letters to six by adding two synthetic bases called X and Y to the DNA of Escherichia coli bacteria.

However, the resulting semisynthetic organism grew slowly, and cannot keep the synthetic base pair in their code indefinitely as they divided.

In the new study, the researchers optimized a tool called a nucleotide transporter, making it much easier for the semisynthetic organism to grow and divide while holding on to X and Y.

The researchers also described in the U.S. journal Proceedings of the National Academy of Sciences how they improved their previous version of Y.

In addition, they created a "spell check" system for the organism using a popular gene-editing tool called CRISPR-Cas9 that will see a genetic sequence without X and Y as a foreign invader.

As a result, a cell that dropped X and Y would be marked for destruction, leaving the scientists with an organism that could hold on to the new bases.

Their new semisynthetic organism was found to be able to keep X and Y in its genome after dividing 60 times, leading the researchers to believe it can hold on to the base pair indefinitely.

Romesberg emphasized that this work is only in single cells and is not meant to be used in more complex organisms, adding that the actual applications for this semisynthetic organism are "zero" at this point.

Although the organism now can only be used to store genetic information, the work could be used to create new functions for single-celled organisms that play important roles in drug discovery and much more in the future, he noted.

"With the virtually unrestricted ability to maintain increased information, the optimized SSO (semisynthetic organism) now provides a suitable platform for efforts to ... create organisms with wholly unnatural attributes and traits not found elsewhere in nature," they wrote in their paper.

"Moreover, semisynthetic organisms that stably harbor such a UBP (unnatural base pair) in their DNA could ... lay the foundation for achieving the central goal of synthetic biology: the creation of new life forms and functions."