Professor Lenski’s Amazing Citrate-Eating E. coli

These guys again

You’ve heard of Richard Lenski’s long-term E. coli experiment before, I assume. It’s widely cited as a counterexample to a subset of creationist claims, and is particularly famous for Andrew Schlafly’s hillarious attempt to challenge Lenski’s findings in 2008. RationalWiki summarises what you should already know:

On June 9, 2008, the New Scientist published an article describing preliminary results of a long-running experiment started by Lenski [ED: link]. Lenski and his team had taken a single strain of the bacterium E. coli, separated its descendants into twelve populations, and proceeded to observe their mutations over the course of twenty years (a process discussed on Lenski’s website). The E. coli were fed a measured amount of glucose every day. At one point, one of the populations exploded far beyond the parameters of the experiment. Lenski eventually discovered that this population had evolved the ability to “eat” citrate, an organic molecule which was part of the solution the E. coli lived in, but which E. coli cannot normally digest. Thus, evolution had been visibly observed, with an exquisite amount of evidence establishing the timeline along the way. Not only that, but the experiment was repeatable; Lenski started new experiments with the frozen “archives” of the population which exploded, and found that beyond a certain point, that particular population of E. coli were highly likely to evolve the ability to digest citrate. The paper also highlighted the role of historical contingency in evolution and the role of potentiating mutations.

There is an additional, less commonly known but still important fact to note: your average E. coli can already metabolise citrate, just not in the presence of oxygen. Indeed, not doing so is a defining characteristic of the species* – does this experiment then qualify as the creation of a new “kind” of organism, I wonder?

Anyway, that’s what we already knew. While the appearance of citrate metabolism was well-documented, with huge quantities of data to wade through only now (with a new paper in Nature) do we have an insight into the changes at the genetic level that allowed the phenotypic changes be observed. Perhaps in a desire to become the next Schlafly, Brian Thomas writes Bacterial ‘Evolution’ Is Actually Design in Action. Continue reading