How selective breeding of bacteria continues to tell us a lot about evolution

bacteriaby adrigu

Researchers track evolution through snapshots of 40,000 generations
[Via Ars Technica]

In 1988, Richard Lenski’s lab began an experiment. A set of 12 bacterial cultures were started, but only given enough sugar to keep them growing for a few hours. The next day, the bacteria were again given another burst of sugar. And the process has been repeated every day since. The goal? To be able to follow major evolutionary innovations as bacteria try to outcompete their peers under near-starvation.

Back in 2008, one of the 12 cultures had its big breakthrough, a sudden burst of growth powered by citrate, a chemical that was present in the mix, but not normally used by bacteria (a result that was hilariously contested by the founders of Conservapedia). Now, Lenski is benefitting from a technology that didn’t exist when he started the work—whole genome sequencing—and reconstructing exactly how the bacteria evolved the new ability.

The team behind the latest work took advantage of the fact that the experiment has involved taking snapshots of the bacteria every few thousand generations, simply by siphoning a few off and sticking them in the freezer. These bacteria can be used to figure out what the status of the genomes were at a given generation, or even grown again, to see whether the same evolutionary history can take place.


Now that we can easily sequence the entire genomes of bacteria quite easily, we are gaining a strong look at the types of DNA changes that natural selection produces.

Gene duplications and altered gene regulation appear to be major players in the evolutionary process.

They also created a clade tree that is every bit as complex as many  of those seen in the wild, with one entire clade becoming extinct.

And what is interesting is that even though we can see an obvious change in the way the bacteria work, we still do not always know exactly which DNA changes are responsible. Thus paving the way for even more work.

But the most important thing is that they may have actually described a three step evolutionary process that could be very common: potentiation, actualization and refinement..

This three-step process—in which potentiation makes a trait possible, actualization makes the trait manifest, and refinement makes it effective—is probably typical of many new functions.

While not exactly Earth-shaking, it is nice to see actually results that support this view.