Scientists created bacteria with a synthetic genome. Is this artificial life?

Scientists have created a living organism whose DNA is entirely human-made — perhaps a new form of life, experts said, and a milestone in the field of synthetic biology.

Researchers at the Medical Research Council Laboratory of Molecular Biology in Britain reported last week that they had rewritten the DNA of the bacteria Escherichia coli, fashioning a synthetic genome four times larger and far more complex than any previously created.

The bacteria are alive, though unusually shaped and reproducing slowly. But their cells operate according to a new set of biological rules, producing familiar proteins with a reconstructed genetic code.

The achievement one day may lead to organisms that produce novel medicines or other valuable molecules, as living factories. These synthetic bacteria also may offer clues as to how the genetic code arose in the early history of life.

“It’s a landmark,” said Tom Ellis, director of the Center for Synthetic Biology at Imperial College London, who was not involved in the new study. “No one’s done anything like it in terms of size or in terms of number of changes before.”

Each gene in a living genome is detailed in an alphabet of four bases, molecules called adenine, thymine, guanine and cytosine (often described only by their first letters: A, T, G, C). A gene may be made of thousands of bases.

Genes direct cells to choose among 20 amino acids, the building blocks of proteins, the workhorses of every cell. Proteins carry out a vast number of jobs in the body, from ferrying oxygen in the blood to generating force in our muscles.

Nine years ago, researchers built a synthetic genome that was 1 million base pairs long. The new E. coli genome, reported in the journal Nature, is 4 million base pairs long and had to be constructed with entirely new methods.

The new study was led by Jason Chin, a molecular biologist at the MRC laboratory, who wanted to understand why all living things encode genetic information in the same baffling way.

The production of each amino acid in the cell is directed by three bases arranged in the DNA strand. Each of these trios is known as a codon. The codon TCT, for example, ensures that an amino acid called serine is attached to the end of a new protein.

Since there are only 20 amino acids, you’d think the genome only needs 20 codons to make them. But the genetic code is full of redundancies, for reasons that no one understands.

Amino acids are encoded by 61 codons, not 20. Production of serine, for example, is governed by six different codons. (Another three codons are called stop codons; they tell DNA where to stop construction of an amino acid.)

Like many scientists, Chin was intrigued by all this duplication. Were all these chunks of DNA essential to life?

“Because life universally uses 64 codons, we really didn’t have an answer,” Chin said. So he set out to create an organism that could shed some light on the question.

After some preliminary experiments, he and his colleagues designed a modified version of the E. coli genome on a computer that only required 61 codons to produce all of the amino acids the organism needs.

Instead of requiring six codons to make serine, this genome used just four.

Much to their relief, the altered E. coli did not die. The bacteria grow more slowly than regular E. coli and develop longer, rod-shaped cells. But they are very much alive.