The Life and (Long) Times of Bugs

If there’s one thing that Jurassic Park taught us, it’s that evolution is a long, drawn-out process*. Novel traits evolve in different species over millions of years, so most human scientists aren’t around long enough to see them happen in real time. But what if we could study evolution on a slightly smaller scale? Say, in bacteria such as Escherichia coli? Researcher’s from Michigan, Texas and Calgary took twelve founder E. coli bacteria and grew them in twelve separate soups, the main ingredients of which were glucose and citrate – glucose as an energy source and citrate as a chelating agent to scavenge any contaminating metals out of the soup and prevent them from adversely affecting bacterial growth. Every day for the next 20 years, a tiny volume (one ten thousandth of a litre) from each soup was siphoned off and used to start up a new soup.

These twelve seed bacteria reproduced through 40,000 generations of progeny, with several distinct evolutionary arms arising within each of the twelve cultures. Each different arm had varying degrees of success – for example, one died out after 15,000 generations. Each arm was characterised by a particular set of mutations, which accumulated as time progressed. Chunks of DNA were deleted or inserted, single letters in the DNA code got changed and chromosomes were juggled about. The most startling innovation that evolved out of the sum of these mutations was that one arm acquired the ability to exploit citrate, the chelating agent in the soup, as an energy source. Normally, E.coli can’t use citrate under well-aerated conditions, since they lack a functional citrate transporter – in fact, this is a hallmark of E. coli as a species. Thus, a trait evolved that went against a defining property of a species: oh evolution, you beautiful queen.

While this experiment still has a little way to go before it breaks any records as, “the longest experiment of all time”, a title currently held by a Pitch Drop experiment started in 1927, it does stand out as a sterling example of science at perhaps its most interesting.

*Also, that velociraptor’s are the most evil of all dinosaurs

Blount, Z., Barrick, J., Davidson, C., & Lenski, R. (2012). Genomic analysis of a key innovation in an experimental Escherichia coli population Nature, 489 (7417), 513-518 DOI: 10.1038/nature11514

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