人工生命一步美科学家初步培育成“人造细胞”

Scientists announced a bold step Thursday in the enduring quest to create artificial life. They've produced a living cell powered by manmade DNA. While such work can evoke images of Frankenstein-like scientific tinkering, it also is exciting hopes that it could eventually lead to new fuels, better ways to clean polluted water, faster vaccine production and more.

Is it really an artificial life form?

The inventors call it the world's first synthetic cell, although this initial step is more a re-creation of existing life — changing one simple type of bacterium into another — than a built-from-scratch kind.

Maryland genome-mapping pioneer J. Craig Venter said his team's project paves the way for the ultimate, much harder goal: designing organisms that work differently from the way nature intended for a wide range of uses. Already he's working with ExxonMobil in hopes of turning algae into fuel.

And the report, being published Friday in the journal Science, is triggering excitement in this growing field of synthetic biology.

"It's been a long time coming, and it was worth the wait," said Dr. George Church, a Harvard Medical School genetics professor. "It's a milestone that has potential practical applications."

The project has overcome some hurdles in engineering larger genomes that will help push forward the field, said biological engineer Dr. Ron Weiss, a Massachusetts Institute of Technology leader in synthetic biology.

"It's an important step," said Weiss. Even though the manmade DNA needed an already living cell to start working, eventually it reproduced and "all elements in the cells after some amount of time can be traced to this initial artificial DNA. That's a great accomplishment."

Scientists for years have moved single genes and even large chunks of DNA from one species to another. Venter aimed to go further. A few years ago, his team transplanted an entire natural genome, all of an organism's genes, one bacterium into another and watched it take over — turning a goat germ into a cattle germ.

Next, the researchers built from scratch another, smaller bacterium's genome, using off-the-shelf laboratory-made DNA fragments.

Friday's report combines those two achievements to test a big question: Could synthetic DNA really take over and drive a living cell? Somehow, it did.

"This is transforming life totally from one+ species into another by changing the software," said Venter, using a computer analogy to explain the DNA's role.

The researchers picked two species of Mycoplasma, simple germs that contain a single chromosome and lack the cell walls that form barriers in other bacteria. First, they chemically synthesized the genome of M. mycoides, that goat germ, twice as large as the germ genome they'd previously built.

Then they transplanted it into a living cell from a different Mycoplasma species, albeit a fairly close cousin.

At first, nothing happened. The team scrambled to find out why, creating a genetic version of a computer proofreading program to spell-check the DNA fragments they'd pieced together. The result: They found that a typo in the genetic code, in one of the synthetic genome's million chemical base pairs, was rendering the manmade DNA inactive, delaying the project three months to find and restore that bit.

"It shows you how accurate it has to be, one letter out of a million," Venter said.

That fixed, the transplant worked. The recipient cell started out with synthetic DNA and its original cytoplasm, but the new genome "booted up" that cell to start producing only proteins that normally would be found in the copied goat germ. It reproduced into a small colony of germs in a lab dish. The researchers had tagged the synthetic DNA to be able to tell it apart, and confirmed that those new ones really looked and behaved like M. mycoides, not the recipient cell