Time in a bottle: Scientists watch evolution unfold
Posted by Xeno on October 19, 2009
A 21-year Michigan State University experiment that distills the essence of evolution in laboratory flasks not only demonstrates natural selection at work, but could lead to biotechnology and medical research advances, researchers said.Charles Darwin’s seminal Origin of Species first laid out the case for evolution exactly 150 years ago. Now, MSU professor Richard Lenski and colleagues document the process in their analysis of 40,000 generations of bacteria, published this week in the international science journal Nature. Lenski, Hannah Professor of Microbial Ecology at MSU, started growing cultures of fast-reproducing, single-celled E. coli bacteria in 1988. If a genetic mutation gives a cell an advantage in competition for food, he reasoned, it should dominate the entire culture. While Darwin’s theory of natural selection is supported by other studies, it has never before been studied for so many cycles and in such detail.
“It’s extra nice now to be able to show precisely how selection has changed the genomes of these bacteria, step by step over tens of thousands of generations,” Lenski said.Lenski’s team periodically froze bacteria for later study, and technology has since developed to allow complete genetic sequencing. By the 20,000-generation midpoint, researchers discovered 45 mutations among surviving cells. Those mutations, according to Darwin’s theory, should have conferred some advantage, and that’s exactly what the researchers found.
The results “beautifully emphasize the succession of mutational events that allowed these organisms to climb toward higher and higher efficiency in their environment,” noted Dominique Schneider, a molecular geneticist at the Université Joseph Fourier in Grenoble, France.Lenski’s long-running experiment itself is uniquely suited to answer some critical questions — such as whether rates of change in a bacteria’s genome move in tandem with its fitness to survive.
“The coupling between genomic and adaptive evolution is complex and can be counterintuitive,” Lenski concluded. “The genome was evolving along at a surprisingly constant rate, even as the adaptation of the bacteria slowed down a lot. But then suddenly the mutation rate jumped way up, and a new dynamic relationship was established.” …
- via eurekalert