Scientists in San Diego have achieved a major milestone in the effort to craft artificial organisms: A microbe whose genetic material included some lab-made instructions was able to live, reproduce and synthesize proteins that included molecules never before used by life.

The development, described Wednesday in a paper in the journal Nature, is a step toward a world in which scientists can engineer organisms capable of producing highly specialized proteins that may be used to improve medicines, construct new materials and perhaps change the functions of cells.

“This is the edge of science,” said Andrew Ellington, a biochemist at the University of Texas at Austin who was not involved in the research. “We are better learning how to engineer living systems.”

In 2014, the San Diego scientists, led by chemist Floyd Romesberg of the Scripps Research Institute, rewrote the genetic material for a strain of E. coli to include a new pair of bases, dubbed dNaM and dTPT3 but informally known as X and Y.

Though the resulting microbe population wasn’t stable (they usually lost their X and Y bases after a few days) these were the first organisms in the history of life to include a new base pair in their DNA.

In their latest experiment, Romesberg’s team instructed the cells to synthesize proteins from “noncanonical” amino acids – hundreds of molecules that can be found in nature or the lab but are not naturally used by organisms. The semi-synthetic cells were able to produce artificial proteins almost as efficiently as their unmodified parents.

“This last step of the adding an unnatural base pair to add an unnatural amino acid into a protein is sort of the Holy Grail of what we’ve been trying to do the whole time,” said Yorke Zhang, a graduate student in Romesberg’s lab who designed, performed and analyzed the experiment.