The genetic code is what life everywhere uses to convert the information contained in DNA into specific protein sequences. With minor variations, the same genetic code is used by every living thing on Earth, suggesting it was already present in the last common ancestor of all of it. It's not an easy thing to change, because so many things in every cell depend on it.
Nevertheless, some preliminary steps have been taken. Researchers have managed to add some new amino acids to a bacterial cell and were able to make proteins that were one amino acid less than usual. But it's a slog; for some of this work, people have had to re-engineer every single gene in a bacterial genome.
Now, researchers have found a way to operate two separate genetic codes simultaneously, avoiding the need to do any work to compensate for altering the code that every protein in a cell relies on. They didn't test it in an actual cell, and it might cause some problems there. But it's a creative solution that should accelerate some synthetic biology work.
