The evolutionary process has never been directly observed for so many generations and in such details as in Richard Lenski's experiment on bacteria that now features more than 60,000 generations of E. coli.
June 7, 2014
Worldwide, researchers seeking solutions to antibiotic resistance and working on other projects are unquestionably inspired by the work of Richard Lenski, an MSU AgBioResearch evolutionary biologist and Hannah distinguished professor of microbial ecology. His long running experiment with Escherichia coli (E. coli) began in 1988, when he placed 12 populations of bacteria — all from the same ancestral strain — into 12 flasks with the same simple medium to see how similarly or differently they would evolve.
Originally, Lenski wanted to keep the experiment going for at least a year, which would have spanned about 2,000 bacterial generations. Now, 26 years later, the project — known as the Long-Term Evolution Experiment (LTEE) —has reached 60,000 generations. It is currently supported by a National Science Foundation grant for long-term research in environmental biology. Though Charles Darwin’s theory of natural selection has been confirmed by many lines of scientific evidence, the evolutionary process has never been directly observed for so many generations and in such detail as in Lenski’s experiment. The work is set apart by the many questions that can be answered by the long-running study. It has led to new insights about the speed of adaptation and the origin of new capabilities. It also revealed an evolutionary tension between shortterm success and long-term persistence — more adaptable bacterial types sometimes prevail over lineages that hold a short-term competitive advantage.
In addition to taking advantage of the speed with which bacteria reproduce and evolve, Lenski and his research team periodically freeze samples of the bacteria for future study in what he calls a “frozen fossil record.” Over the years, powerful new technologies were invented to analyze the DNA that is found in every living cell, culminating in the ability to sequence entire genomes.
“I had no idea then that new technologies would help us find all of the changes in the DNA,” Lenski said. “But since we saved bacterial samples throughout the experiment in a deep freezer, it’s like time travel because we can now directly compare their genomes across tens of thousands of generations.”
LTEE is not the only project in Lenski’s lab. In another recent experiment, Lenski’s team showed for the first time that a virus called “Lambda” could evolve to find a new way to enter host cells, an innovation that took four mutations to accomplish. Fortunately, Lambda is not dangerous to humans — instead, it infects E. coli bacteria. However, the research provides a quintessential model for understanding how viruses evolve complex and potentially deadly new traits.
Lenski’s work on evolution also has crossed into the digital world. He has teamed up with computer scientists to use computer programs that selfreplicate, mutate and evolve new abilities. “My colleagues developed this biology inspired software that we can use to explore evolutionary processes,” he said. “At the same time, they are using these evolutionary processes to help develop new technologies in the areas of networks, communication systems and robotics.”
While Lenski continues to pursue basic research with the bacteria, the LTEE project has led others to work toward various applications — from strain improvement and microbial forensics on the biology side, to new strategies for harnessing evolutionary mechanisms on the computational side.
“I think the major benefit of these experiments is that they give us a better understanding of evolution because it is experimentally tested, not an interpretation,” said James Tiedje, University Distinguished Professor of plant, soil and microbial sciences and director of the Center for Microbial Ecology. “Rich sees evolution in real time, and because he has replicates, he can see the differences as well as similarities of evolutionary outcomes. This is directly relevant to development of antibiotic resistances, and his basic work can help with finding solutions to the appearance and spread of resistances of all types.”
Jane L. Depriest or Holly Whetstone