The research team succeeded in creating a man-made copy of the genome for a bacterium, the first time that's been done. A genome is the complete set of DNA in the chromosomes of a living organism, the instruction set for how an organism works.

But while they were able to copy the genome of an existing organism, they weren't able to create a brand new one. Essentially, they managed to write the "software code" for a bacterium but they haven't yet figured out how to turn it on and make it live.

Once that's possible, it opens the door to building made-to-order organisms that could do things natural organisms don't: plants that take up large amounts of carbon from the atmosphere to slow global warming, microbes that turn grass clippings into fuel, bacteria that eat sugar and produce medicine. Some researchers believe that's a long way off.

"These guys have not synthesized a brand new life form," - says Jim Collins, a professor of biomedical engineering at Boston University. Science still has a long way to go to understanding the underlying biology of life necessary to do that, he says.

There are "multiple barriers to this," - Venter acknowledges. "But we're confident that they can be overcome."

Another worry: Once this technology becomes commonplace, it can be used to create both good organisms and dangerous ones, says David Magnus, director of Stanford University's Center for Biomedical Ethics.

Venter's team has already genetically modified the bacterium to make it non-infectious.