Georgia Tech researchers say they've resurrected a 500-million-year-old gene from bacteria and inserted it into modern-day Escherichia coli (E. coli) bacteria.

The resurrected bacterium has been growing for more than 1,000 generations, providing scientists a chance to observe evolution in action, the university announced Wednesday.

"This is as close as we can get to rewinding and replaying the molecular tape of life," scientist Betul Kacar said of the effort, dubbed paleo-experimental evolution. "The ability to observe an ancient gene in a modern organism as it evolves within a modern cell allows us to see whether the evolutionary trajectory once taken will repeat itself or whether a life will adapt following a different path."

The researchers began by determining the ancient genetic sequence of Elongation Factor-Tu (EF-Tu), an essential protein in E. coli. After achieving the difficult task of replacing the modern gene in E. coli with the ancient gene in the correct chromosomal order and position, Kacar produced eight identical bacterial strains and allowed "ancient life" to re-evolve.

The bacteria composed of both modern and ancient genes survived, but grew about two times slower than its counterpart composed of only modern genes, he said.

"The altered organism wasn't as healthy or fit as its modern-day version, at least initially, and this created a perfect scenario that would allow the altered organism to adapt and become more fit as it accumulated mutations with each passing day," Kacar said.

After 500 generations, the scientists sequenced the genomes of all eight lineages and found that not only did the fitness levels increase to nearly modern-day levels, some of the altered lineages actually became healthier than their modern counterpart.

The ancient gene had not yet mutated to become more similar to its modern form, they said, but rather the bacteria found a new evolutionary trajectory to adapt.

The finding could answer the question of whether an organism's history limits its future and evolution always leads to a single, defined point, or whether evolution has multiple solutions to a given problem, Kacar said.