Taking a significant step toward the creation of synthetic forms of life, researchers reported that they had manufactured the entire genome of a bacterium by stitching together its chemical components.

Scientists had previously constructed the complete DNA of viruses, but this is the first time it has been done for bacteria, which are far more complex. The genome is more than 10 times as long as the longest piece of DNA ever synthesized.

The feat is a watershed for the emerging field called synthetic biology, which involves the design of organisms to perform particular tasks, like making biofuels. Synthetic biologists envision being able to design an organism on a computer, press the “print” button to have the necessary DNA made and then put that DNA into a cell to produce a custom-made creature.

“What we are doing with the synthetic chromosome is going to be the design process of the future,” said J Craig Venter, the boundary-pushing gene scientist.

Dr Venter assembled the team that made the bacterial genome as part of his well-publicised quest to create the first synthetic organism. The work was published online Thursday by the journal Science.

But there are concerns that synthetic biology could be used to make pathogens, or that errors by well-intended scientists could produce organisms that run amok. The genome of the smallpox virus can in theory now be synthesized using the techniques reported on Thursday since it is only about one-third the size of the genome manufactured by Dr Venter’s group.

In any case, there are many hurdles to overcome before Dr Venter’s vision of “life by design” is realised. The synthetic genome made by Dr Venter’s team was not designed from scratch, but rather was a copy, with only a few changes, of the genetic sequence of a natural bacterium called Mycoplasma genitalium.

Moreover, Dr Venter’s team, led by a Nobel laureate, Hamilton O Smith, has yet to accomplish the next — and biggest — step. That would be to insert the synthetic chromosome into a living microbe and have it “boot up” and take control of the organism’s functions.

If that happened, it would be considered by some to be the creation of the first synthetic organism. The failure to achieve that tempered the reaction of some outside scientists to the announced achievement.

“Right now, all they’ve done is shown they can buy a bunch of DNA and put it together,” said George M Church, a professor of genetics at Harvard Medical School.

Dr Venter’s team last year reported successfully doing such a chromosome transplant, but it was with the natural genome of one type of Mycoplasma transplanted into another species of that bacterium.

Dr Venter said in a telephone news conference Thursday that each pair of donor genome and recipient cell presented unique problems. The scientists also think they interrupted the functioning of one crucial gene, a correctable problem.

“It’s not a slam dunk or we would be announcing it today,” Dr Venter told reporters. Still, he said, “I will be equally surprised and disappointed if we can’t do it in 2008.”

The bacterial genome that was synthesised consisted of 582,970 base pairs, the chemical units of the genetic code represented by the letters A, C, G and T. The longest stretch of synthetic DNA reported in a scientific paper was about 32,000 bases long, though some companies say they have made ones with about 50,000. -Reuters

The machines that string bases together make many errors, so it is impractical to make a string of more than 50 to 100 bases at once. But some companies — the foundries of the biotechnology era — now make genes thousands of bases long by splicing the shorter strings.

The Venter team ordered 101 such sequences, each 5,000 to 7,000 bases long, from these companies. It then joined them into ever-bigger pieces. Finally, four big pieces were put into yeast, which<