Venter and his colleagues modified the DNA of a Mycoplasma, a kind of bacteria, creating a final strand composed of roughly one million "base pairs," the components which make up DNA.

The human genome, by comparison, contains more than three billion base pairs.

The scientists then injected the synthetic DNA into another Mycoplasma bacterium, which had already had its DNA removed. The bacterium began to grow and reproduce, though some of the synthesized genes didn't work properly.

Exxon contract

Venter hopes the technology could eventually be used to make new and less expensive vaccines, pharmaceutical drugs and biofuels.

The energy giant Exxon awarded Venter's company a contract, worth up to $600m, to use the technology to generate biofuels from algae.

Similar research has been conducted in the past: Scientists have constructed viruses using synthesised DNA. But Venter's work is the first to replicate such a long strain of DNA.

Environmental groups, concerned about the widespread adoption of biofuels, are wary of the synthetic DNA. Friends of the Earth issued a statement calling it "dangerous new technology".

Barack Obama, the US president, asked his bioethics council to study the potential ethical implications of artificial DNA.