Scientists have completely rewritten the genetic code of a bacteria - and the next step might be to make something completely new, from scratch.
In future, "recoded" microbes could be used to create new molecules with many different purposes, from fighting disease to manufacturing materials with unusual properties.
The research represents a leap forward in the emerging field of synthetic biology.
"This is the first time the genetic code has been fundamentally changed," said Dr Farren Isaacs from Yale University in the US, whose work is reported in the journal Science.
"Creating an organism with a new genetic code has allowed us to expand the scope of biological function in a number of powerful ways."
Conducting experiments on Escherichia coli (E.coli) bacteria, the scientists succeed in changing the basic rules of biology.
The genetic code that provides the instructions for making proteins consists of four "letters" in the form of nucleotides, the essential components of DNA.
These are arranged in different combinations of three-letter "words" called codons. Amino acids, the building blocks of proteins, are encoded by 64 codon arrangements.
The US team from Yale and Harvard universities expanded on nature's handiwork by substituting different codons throughout the E.coli genome. They were also able to reintroduce entirely new "letters" to create novel amino acids.
With the new genome, E.coli bacteria were able to resist viral infection by limiting production of proteins used by viruses to infect cells.
The work sets the stage to convert recoded microbes into living factories capable of manufacturing new classes of exotic proteins and polymers, say the scientists.
"Since the genetic code is universal, it raises the prospect of recoding genomes of other organisms," said Dr Isaacs.
"This has tremendous implications in the biotechnology industry and could open entirely new avenues of research and applications."