The results, published in the current issue of Nature, are revealed through an in-depth, genomics-based analysis that decodes how E. coli bacteria figured out how to supplement a traditional diet of glucose with an extra course of citrate.
“It’s pretty nifty to see a new biological function evolve,” said Zachary Blount, postdoctoral researcher in MSU’s BEACON Center for the Study of Evolution in Action. “The first citrate-eaters were just barely able to grow on the citrate, but they got much better over time. We wanted to understand the changes that allowed the bacteria to evolve this new ability. We were lucky to have a system that allowed us to do so.”
Normal E. coli can’t digest citrate when oxygen is present. In fact, it’s a distinct hallmark of E. coli. They can’t eat citrate because E. coli don’t express the right protein to absorb citrate molecules.
To decipher the responsible mutations, Blount worked with Richard Lenski, MSU Hannah Distinguished Professor of Microbiology and Molecular Genetics. Lenski’s long-term experiment, cultivating cultures of fast-growing E. coli, was launched in 1988 and has allowed him and his teammates to study more than more than 56,000 generations of bacterial evolution.
The experiment demonstrates natural selection at work. And because samples are frozen and available for later study, when something new emerges scientists can go back to earlier generations to look for the steps that happened along the way.