It’s a project 500 million years in the making. Only this time, instead of
playing on a movie screen in Jurassic Park, it’s happening in a laboratory at
the Georgia Institute of Technology.
Using a process called paleo-experimental evolution, Georgia Tech
researchers have resurrected a 500-million-year-old gene from bacteria and
inserted it into modern-day Escherichia
coli (E. coli) bacteria. This
bacterium has now been growing for more than 1,000 generations, giving the
scientists a front row seat to observe evolution in action.
“This is as close as we can get to rewinding and replaying the molecular
tape of life,” said scientist Betül Kaçar, a NASA astrobiology postdoctoral
fellow in Georgia Tech’s NASA Center for Ribosomal Origins and 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.”
In 2008, Kaçar’s postdoctoral advisor, Associate Professor of Biology Eric
Gaucher, successfully determined the ancient genetic sequence of Elongation
Factor-Tu (EF-Tu), an essential protein in E.
coli. EFs are one of the most abundant proteins in bacteria, found in all
known cellular life and required for bacteria to survive. That vital role made
it a perfect protein for the scientists to answer questions about evolution.
After achieving the difficult task of placing the ancient gene in the
correct chromosomal order and position in place of the modern gene within E. coli, Kaçar produced eight identical
bacterial strains and allowed “ancient life” to re-evolve. This chimeric
bacteria composed of both modern and ancient genes survived, but grew about two
times slower than its counterpart composed of only modern genes.
“The altered organism wasn’t as healthy or fit as its modern-day version, at
least initially,” said Gaucher, “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.”
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The growth rate eventually increased and, after the first 500 generations,
the scientists sequenced the genomes of all eight lineages to determine how the
bacteria adapted. Not only did the fitness levels increase to nearly modern-day
levels, but also some of the altered lineages actually became healthier than
their modern counterpart.
When the researchers looked closer, they noticed that every EF-Tu gene did
not accumulate mutations. Instead, the modern proteins that interact with the
ancient EF-Tu inside of the bacteria had mutated and these mutations were
responsible for the rapid adaptation that increased the bacteria’s fitness. In
short, the ancient gene has not yet mutated to become more similar to its
modern form, but rather, the bacteria found a new evolutionary trajectory to
adapt.
These results were presented at the NASA International Astrobiology Science
Conference. The scientists will continue to study new generations, waiting to
see if the protein will follow its historical path or whether it will adopt via
a novel path altogether.
“We think that this process will allow us to address several longstanding
questions in evolutionary and molecular biology,” said Kaçar. “Among them, we
want to know if an organism’s history limits its future and if evolution always
leads to a single, defined point or whether evolution has multiple solutions to
a given problem.”
Source: Georgia Institute of Technology