Escherichia coli, researchers incorporated several unnatural amino acids into bacterial proteins. STEVE GSCHMEISSNER/Science Source New approach to rewriting bacteria’s genetic code could lead to novel medicines Jun. 3, 2021 , 4:10 PM Virtually all living organisms construct their proteins from combinations of 20 different amino acids. To add new amino acids to the mix, scientists have re-engineered genes and other bits of protein-building machinery, resulting in proteins with unique chemical properties useful in making drugs. But the work is laborious and can typically only add one new amino acid at a time. Now, researchers have opened the floodgates to doing much more. They report today that a broad rewrite of a bacterium’s genome lets them add numerous novel amino acids to one protein. The work could open new ways to synthesize antibiotics and antitumor drugs.