Scientists in the US have created the first living organisms that can thrive with an expanded genetic code, marking a significant step towards the creation of entirely new life forms. Researchers at the Scripps Research Institute in California modified common E. coli bacteria to carry a six-letter genetic alphabet, adding two synthetic molecules called X and Y to the natural four letters (G, T, C, A).
The work, published in the journal Proceedings of the National Academy of Sciences, aims to eventually program these microbes to produce novel proteins that could be used to develop new drugs and materials. The modified cells represent a 'stable form of semi-synthetic life' and lay the foundation for achieving the central goal of synthetic biology: creating new life forms and functions, according to the researchers.
Lead researcher Floyd Romesberg explained that the microbes are engineered to require a constant supply of the synthetic X and Y molecules, which are not found in nature. This acts as a failsafe: if the bacteria escape the lab, they will die without these molecules. Romesberg noted that unlike the fictional dinosaurs in Jurassic Park, these cells cannot evolve to produce X and Y on their own.
This is not the first attempt by Romesberg's team; in 2014 they created similar organisms, but those were sickly and died out quickly. Over the past two years, the team made three crucial fixes, including modifying the microbe's immune system to destroy any DNA lacking the synthetic bases. The result is that the bacteria can now hold the new genetic material indefinitely.
Currently, the synthetic bases do not code for anything, but the next stage is to have the microbes read the extra genetic material to produce new kinds of proteins not found in nature. 'This will blow open what we can do with proteins,' Romesberg said. Paul Freemont, a synthetic biology expert at Imperial College London, described the work as a major step forward, leading to the concept of semi-synthetic living systems engineered for specific functions.
