The process was started in late 2002, Dr. Venter said, and undoubtedly cost millions of dollars. That led some scientists to question why someone would want to synthesize an entire organism. Scientists can already make useful organisms  including some that are now starting to be make biofuels  by modifying existing ones using genetic engineering.

“It’s not entirely clear to me what the immediate purpose of doing something like this is,” said Jeremy Minshull, chief executive of DNA 2.0, a company that supplied some of the DNA stretches to the Venter team. “To some extent, it’s something that was driven by ‘I want to be the first person to do it.’ ”

Right now, Mr. Minshull said, scientists do not know enough about how living things work to design an entire genome: “Now our synthetic capability way outpaces our understanding of what we want to do.”

For now, that is the case, Dr. Venter concedes. He has a company, Synthetic Genomics, that is using genetic engineering to produce biofuels. It is using organisms other than Mycoplasma genitalium, which was chosen for the synthetic genome project because its genome is tiny, one-tenth the size of the genomes of some other bacteria. But Mycoplasma is not suited to industrial production.

Still, Dr. Venter and some other scientists say that DNA synthesis is following the path of computer chips, with capability rising rapidly and cost  now about $1 per base  falling swiftly. At some point, they say, it will become faster and cheaper for scientists to design and synthesize an organism from scratch rather than cut and paste genes from one organism to another, just as it is sometimes easier for a writer to type a fresh draft rather than edit an existing one.

The ability to synthesize genomes would allow for more scientific experimentation. Dr. Venter said he would now be able to create organisms missing dozens of genes to answer the initial question that sparked the research ten years ago: What is the minimum set of genes needed for life?

Dr. Venter, who runs the nonprofit J. Craig Venter Institute in Rockville, Md., has been a pioneer in genomics. He is best known for sequencing the human genome in a race with the publicly funded Human Genome Project. The method his team used was novel at the time, but is now widely accepted. It turned out that the genome his team sequenced was his own, making Dr. Venter the first person to have his complete DNA sequence published.