Washington ? Talk about identity theft: Scientists changed one species of bacteria into another by performing a complete gene swap.

It’s a step in the quest to one day create artificial organisms, part of a bigger project to custom-design microbes that could produce cleaner fuels. But the way it was performed, dubbed a “genome transplant,” has genetics specialists buzzing.

“This is equivalent to changing a Macintosh computer to a PC by inserting a new piece of software,” declared genome-mapping pioneer J. Craig Venter, senior author of the new research published Thursday by the journal Science.

For years, scientists have moved single genes and even large chunks of DNA from one species to another. But Venter’s team transplanted an entire genome, all of an organism’s genes, from one bacterium into another in one fell swoop.

These weren’t complex bacteria, but cousins from a family of small, simple microbes known as Mycoplasma. Nor do the researchers know exactly how the transplant took hold. But somehow the new genes cleanly replaced the old and started working correctly – not very often, but in just enough cells to prove the concept.

The experiment “is a landmark in biological engineering,” said Dr. Barbara Jasny, a deputy editor of Science.

Beyond pushing scientific boundaries, why would switching a goat germ into a cattle germ be useful?

Venter’s self-named institute in Rockville, Md., is trying to create an artificial chromosome – the structure that carries DNA – that contains industrially useful genes such as ones that could help produce alternative fuels.