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Evolving E. coli

25-year experiment sees real-time natural selection

2012 SCIENCE NEWS TOP 25: 23 

A simple flask of bacteria has given scientists a glimpse of evolution in action.

Escherichia coli bacteria that were part of a 25-year evolution experiment acquired a new ability at some point during the study. They can now eat a chemical called citrate in the presence of oxygen. E. coli lost that trait more than 13 million years ago, so when bacteria in one flask — designated Ara-3 (shown) — started gorging on the chemical, scientists were fascinated. Because they had saved samples of multiple generations from the flask, the researchers were able to trace the genetic changes that led the microbes to redevelop citrate-eating capabilities.

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