By Victoria Gill
Science reporter, BBC News
The cells replicated to produce a new strain of Mycoplasma mycoides
In what has been described as a step towards the creation of a synthetic cell, scientists have created a new "engineered" strain of bacteria.
A team successfully transferred the genome of one type of bacteria into a yeast cell, modified it, and then transplanted into another bacterium.
This paves the way to the creation of a synthetic organism - inserting a human-made genome into a bacterial cell.
The team describe the work in the journal Science.
This advance, the researchers say, overcomes the obstacle of making a new inserted genome work inside a recipient cell.
The experiment was carried out by a team that included scientist J Craig Venter, a leading figure in the controversial field of synthetic biology.
Sanjay Vashee, a researcher at the J Craig Venter Institute in Rockville, Maryland, in the US, was one of the authors.
The resulting cell he and his team created went on to undertake multiple rounds of cell division, to produce a new strain of the modified bacteria.
Dr Vashee explained to BBC News that the work overcame a hurdle in the quest to create a fully synthetic organism.
J Craig Venter is a leading figure in this controversial field
"Bacteria have 'immune' systems that protect them from foreign DNA such as those from viruses," he explained.
He and his colleagues managed to disable this immune system, which consists of proteins called restriction enzymes that home in on specific sections of DNA and chop up the genome at these points.
Bacteria can shield their own genomes from this process by attaching chemical units called methyl groups at the points which the restriction enzymes attack.
The scientists modified the original genome of the bacterium Mycoplasma mycoides, whilst it was inside the yeast cell. Then they either attached methyl groups to it, or inactivated the restriction enzyme of the recipient bacterium, before transplanting the genome into its new cell.
One of the team's ultimate aims is to transplant a fully synthetic genome into a bacterial cell - creating bacteria that can be programmed to carry out specific functions - for example, digesting biological material to produce fuel.
Race for life
Researchers at the same institute have already synthesised the complete genome of a bacterium called Mycoplasma genitalium. Dr Vashee described this work as a "logical extension" of that.
He told BBC News that attempts to create a synthetic bacterium by transplanting M. genitalium into a cell were "ongoing".
"We have as of yet no conclusive proof that we have obtained M. genitalium cells after its genome has been put into various recipient cells," he said.
"[But this] is a major advance in our effort to create a synthetic cell."
Dr Vashee continued: "We were very concerned that the differences between the modifications in... bacterial DNA and [yeast] DNA might be an insurmountable barrier, preventing transplantation into bacteria of genomes that were passed through yeast.
"Now we know how to do this."
Critics have expressed reservations about synthetic biology, and the aim to create what has been widely referred to as artificial life.
Many are concerned that the technology to engineer organisms could end up in the wrong hands.
Dr Vashee concluded: "Dr Venter and the team at JCVI continue to work with bioethicists, outside policy groups, [politicians], and the public to encourage discussion and understanding about the societal implications of their work and the field of synthetic genomics."