Sept. 11, 2013
Richard Lenski is a Hannah Distinguished Professor of microbial ecology and an expert in the ecological processes and genetic mechanisms that cause evolutionary change.
I was drawn into the field of microbial evolution as a post-doc in the early 1980s. My previous research was in the field of zoology, studying insects in the mountains of North Carolina. Despite the pleasures of working outdoors, data collection was slow, heavy rains drowned my beetles in their pitfall traps, and it was difficult to imagine feasible experiments that would really test the scientific ideas that most excited me.
As I pondered future directions, I remembered a beautiful experiment that I had encountered as an undergraduate, and the insight it provided into the tension between randomness and direction in evolution.
It was a paper that was published in the journal Genetics in 1943 by Salvador Luria, a biologist, and Mel Delbrück, a physicist-turned biologist, on an experiment sometimes called the Fluctuation Test. In this experiment, E. coli bacteria were used to demonstrate that genetic mutations arise in the absence of selection, rather than being a response to selection. Therefore, Darwin’s theory of natural selection acting on random mutations applies to bacteria, something that was previously unclear to microbiologists. Luria and Delbrück went on to win the Nobel Prize in 1969 for this and related work, which helped set off the modern revolution in molecular biology.
Evolution is like a game that combines luck and skill, and so I thought that perhaps bacteria could teach me some interesting new games.
In 1988, I began an experiment with 12 populations of E. coli—all started from the same ancestral strain and all living in identical environments—to see how similarly or differently they would evolve. I wanted to keep the experiment going for at least a year and about 2,000 bacterial generations, maybe longer. Twenty-five years later, the experiment is still going strong and is up to more than 58,000 generations.
This work is unconventional in that most evolutionary biologists study evolution by examining fossils or by comparing different species. My team and I study evolution by doing experiments where we can watch evolution in action. That means that we have to study fast-reproducing organisms, like bacteria, in order to observe lots of generations.
In my work, I like to ask very basic, fundamental questions—for example, “How reproducible is evolution?” That’s why we’re following not just one, but 12 evolving lineages, all started from the same ancestor and living in the same environment.
Another question is, “How tightly coupled are evolutionary changes in the phenotype and the genome?” Here, we’ve really benefitted from new technologies, including especially the ability to sequence entire genomes of bacteria from various generations of the different lineages and compare them to the ancestor.
Our work on microbial evolution—although it’s been motivated by curiosity—has led others to think about applications to real-world problems in epidemiology, microbial forensics, and strain improvement. I think Darwin would be amazed to see where his ideas have led.
Parts of this piece were taken from a longer article that appeared in the magazine Microbe.