Ancient bacteria brought back to life.

Talk about a good nap. A pair of microbiologists claims to have reawakened ancient bacteria that went to sleep when thunder-footed dinosaurs roamed the landscape.

In an experiment that recalls Jurassic Park, Raul J. Cano and Monica K. Borucki discovered the bacteria preserved within the abdomens of insects encased in pieces of amber. In the last 4 years, they have revived more than 1,000 types of bacteria and microorganisms -- some dating back as far as 135 million years ago, during the age of the dinosaurs.

In the May 19 Science, the two, from California Polytechnic State University in San Luis Obispo, describe resuscitating a species of bacteria from a sample of amber 25 million to 40 million years old.

If future tests duplicate such findings, the hoary bacteria would become the oldest known living organisms, far outlasting the most enduring animals and plants, whose lives span a few centuries or millennia at most.

Like other reports of revived bacteria, the new finding will draw criticism from researchers who believe that organisms cannot survive for millions of years. In past cases, skeptical scientists have dismissed purportedly ancient bacteria as modern contaminants.

But microbiologists familiar with the amber discovery say the work of Cano and Borucki differs from previous efforts in the many precautions that the two took to rule out contamination. "I think the case they make for reviving the spores is a good one. I think they have proven their case beyond a reasonable doubt," says Philipp Gerhardt, a microbiologist from Michigan State University in East Lansing who studies bacterial spores.

"They've done all the controls that seem reasonable," says biochemist Peter Setlow of the University of Connecticut Health Center in Farmington. "But this is not something that can be proved beyond a shadow of a doubt," he adds.

In their paper, Cano and Borucki describe how they removed bacterial spores from a bee entombed in amber found in the Dominican Republic. Certain bacteria form spores as a survival tactic when threatened by a lack of food or water. The bacteria dehydrate and coat themselves with a protein shell that protects the dormant cells.

Cano and Borucki revived the spores in a nutrient solution and grew colonies of bacteria, which they identified as Bacillus sphaericus, a species that exists symbiotically in some bees. To address the contamination issue, they tested for bacteria on the surface of the amber, its interior, the solutions used in the experiment, and key locations in the lab.

Using a technique known as polymerase chain reaction, the scientists copied and sequenced a strand of the B. sphaericus DNA. The purportedly ancient DNA resembled a segment from modern B. sphaericus but did not match exactly, providing further proof that modern bacteria had not contaminated the experiment, the researchers say.

Cano believes the spores survived because the amber kept them dry. Recent work has demonstrated amber's remarkable preserving power. In 1993, Cano reported finding the oldest known DNA from insects in amber.

Although they first found the bacterial spores in 1991, Cano says they waited several years before reporting their work in order to validate the discovery. Because modern forms of the bacteria exist, the ancient types present no danger, he says. But he suggests they may provide new antibiotics or other useful compounds.

Setlow disagrees with the claim that the ancient bacteria may produce new antibiotics. But they could provide scientists with much-needed information about the mutation rate of DNA, a so-called molecular clock used to decipher evolutionary relationships among organisms.