Escherichia coli. Credit: Rocky Mountain Laboratories, NIAID, NIH
A pair of Michigan State University researchers conducted an experiment with the bacterium Escherichia coli intended to help settle a long-standing debate in the evolutionary community. They wrote an article describing their experience and results and posted it on the bioRxiv website.
For many years, scientists in the evolutionary biology community have debated which has more impact on the evolutionary process: diversity or random mutations. In this new effort, Minako Izutsu and Richard Lenski performed an experiment involving the evolution of E. coli bacteria over 300 days that included which tests – diversity or mutation – would have the greatest impact on their evolutionary development.
The experiment involved growing E. coli in their lab where the bacteria were allowed to reproduce under varying conditions for almost a year, long enough for them to produce around 2,000 generations.
Initially, groups of bacteria with varying amounts of genetic diversity were placed in petri dishes and fed glucose and the amino acid D-serine. The degree of diversity ranged from zero, for the cloned samples, to as diverse as the group could make them by mixing and matching the samples before the experiment. All samples were cared for the same way bacteria grew and multiplied, and all were tricked into evolving by having them compete for food with a different strain of E. coli. Testing was done at multiple build points, from 0 to 2000.
Looking at how well different groups adapted, the researchers found that at generation point 50, those who started out as more diverse had a clear advantage – they evolved to better compete for food than those who started out. as less diverse. But as time passed and new generations occurred, the advantage diminished. By the end of the study, the edge was completely gone.
The researchers suggest their experiment shows that benefits derived from initial diversity were quickly lost in subsequent generations, suggesting that random mutations are the main driver of evolution, at least in E. coli.
The researchers’ work will of course not settle the debate, even after their paper has been reviewed and published in a respected journal. Similar experiments will need to be conducted on more complex creatures to see if their results hold up.
Evolution experiment with bacteria challenges conventional wisdom about size and cost of production
Minako Izutsu et al, Experimental Testing of the Contributions of Initial Variation and Novel Mutations to Adaptive Evolution in a Novel Environment, bioRxiv (2022). DOI: 10.1101/2022.05.31.494207
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Quote: Experiment settles longstanding debate about evolution – in E. coli, at least (2022, Jun 17) Retrieved Jun 19, 2022 from https://phys.org/news/2022-06-debate- evolutionin-coli.html
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