New York - A year after creating organisms that use a genetic code different from every other living thing, two teams of scientists have achieved another "synthetic biology" milestone: They created bacteria that cannot survive without a specific man made chemical, potentially overcoming a major obstacle to wider use of genetically modified organisms (GMOs). The advance, reported on Wednesday in Nature, offers what one scientist calls a "genetic firewall" to achieve biocontainment, a means of insuring that GMOs cannot live outside a lab or other confined environment. Although the two labs accomplished this in bacteria, "there is no fundamental barrier" to applying the technique to plants and animals, Harvard Medical School biologist George Church, who led one of the studies, told reporters. "I think we are moving in [that] direction." If the technique succeeds, it could be used in microbes engineered for uses from the mundane to the exotic, such as producing yoghurt and cheese, synthesizing industrial chemicals and biofuels, cleaning up toxic waste, and manufacturing drugs. Microbes are already used for those applications. In some cases they contain genes from an unrelated organism, making them "genetically engineered" or "genetically modified" to, say, gobble up oil spills or produce insulin. But widespread use of such GMOs has been constrained by concerns they could escape into the wild and do damage. In 2013, Church's team announced they had leaped beyond genetic engineering to create "genomically recoded" organisms. Recoding means that one bit of their DNA codes for an amino acid (a building-block of proteins) different from what the identical DNA codes for in every other living thing. The biologists had rewritten the genetic spelling book. In the new studies, teams led by Church and a former colleague, Farren Isaacs, created strains of E coli bacteria that both contain DNA for a manmade amino acid and require synthetic amino acids to survive. Because the amino acids do not exist in nature, said Isaacs, now at Yale University, the resulting "firewall" means any GMOs that escaped a lab, manufacturing facility, or agricultural field would die. Church's team made 49 genetic changes to E coli to make them dependent on the synthetic amino acid. The odds of a microbe undoing all the changes are astronomically high, he calculated. By pairing genomic recoding with this firewall, biologists could create escape-proof microbes which, by incorporating novel amino acids, could produce entirely new types of drugs and polymers, Church said.