New organisms have been formed using the first ever 6-letter genetic code

New organisms have been formed using the first ever 6-letter genetic code
This could be the beginning of a whole new life form.
By Bec Crew
Jan 24 2017

Scientists have engineered the first ever ‘semi-synthetic’ organisms, by breeding E. coli bacteria with an expanded, six-letter genetic code.

While every living thing on Earth is formed according to a DNA code made up of four bases (represented by the letters G, T, C and A), these modified E. coli carry an entirely new type of DNA, with two additional DNA bases, X and Y, nestled in their genetic code.

The team, led by Floyd Romesberg from the Scripps Research Institute in California, engineered synthetic nucleotides – molecules that serve as the building blocks of DNA and RNA – to create an additional base pair, and they’ve successfully inserted this into the E. coli’s genetic code.

Now we have the world’s first semi-synthetic organism, with a genetic code made up of two natural base pairs and an additional ‘alien’ base pair, and Romesberg and his team suspect that this is just the beginning for this new form of life.

“With the virtually unrestricted ability to maintain increased information, the optimised semi-synthetic organism now provides a suitable platform [to] … create organisms with wholly unnatural attributes and traits not found elsewhere in nature,” the researchers report.

“This semi-synthetic organism constitutes a stable form of semi-synthetic life, and lays the foundation for efforts to impart life with new forms and functions.”

Back in 2014, the team announced that they had successfully engineered a synthetic DNA base pair – made from molecules referred to as X and Y – and it could be inserted into a living organism.

Since then, they’ve been working on getting their modified E. coli bacteria to not only take the synthetic base pair into their DNA code, but hold onto it for their entire lifespan.

Initially, the engineered bacteria were weak and sickly, and would die soon after they received their new base pair, because they couldn’t hold onto it as they divided.

“Your genome isn’t just stable for a day,” says Romesberg. “Your genome has to be stable for the scale of your lifetime. If the semisynthetic organism is going to really be an organism, it has to be able to stably maintain that information.”

Over the next couple of years, the team devised three methods to engineer a new version of the E. coli bacteria that would hold onto their new base pair indefinitely, allowing them to live normal, healthy lives.

The first step was to build a better version of a tool called a nucleotide transporter, which transports pieces of the synthetic base pair into the bacteria’s DNA, and inserts it into the right place in the genetic code.

“The transporter was used in the 2014 study, but it made the semisynthetic organism very sick,” explains one of the team, Yorke Zhang.

Once they’d altered the transporter to be less toxic, the bacteria no longer had an adverse reaction to it.



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