The lab-made microbe, a strain of bacteria that is normally found in soil and the human gut, is similar to its natural cousins but survives on a smaller set of genetic instructions.
The bug’s existence proves life can exist with a restricted genetic code and paves the way for organisms whose biological machinery is commandeered to make drugs and useful materials, or to add new features such as virus resistance.
In a two-year effort, researchers at the laboratory of molecular biology, at Cambridge University, read and redesigned the DNA of the bacterium Escherichia coli (E coli), before creating cells with a synthetic version of the altered genome.
The Cambridge team set out to redesign the E coli genome by removing some of its superfluous codons. Working on a computer, the scientists went through the bug’s DNA. Whenever they came across TCG, a codon that makes an amino acid called serine, they rewrote it as AGC, which does the same job. They replaced two more codons in a similar way.
More than 18,000 edits later, the scientists had removed every occurrence of the three codons from the bug’s genome. The redesigned genetic code was then chemically synthesised and, piece by piece, added to E coli where it replaced the organism’s natural genome. The result, reported in Nature, is a microbe with a completely synthetic and radically altered DNA code. Known as Syn61, the bug is a little longer than normal, and grows more slowly, but survives nonetheless.