Year in review: Fluke extinction surprises lab

Accident, not competition, wiped out E. coli


CAUSE OF DEATH  Researchers previously believed that the extinction in one flask of bacteria in a long-term evolution experiment was the result of survival of the fittest. This year, scientists discovered the bacteria's demise was more likely an accident. 


A die-off of bacteria that had been growing for thousands of generations in a carefully controlled lab experiment offered an evolutionary lesson this year: Survival depends not only on fitness but also on luck.

For more than a quarter century, evolutionary biologist Richard Lenski and colleagues have been growing 12 flasks of E. coli at Michigan State University. About 31,000 generations in, some of the bacteria in one flask evolved the ability to use a chemical called citrate as an energy source. Bacteria in that flask that couldn’t eat citrate went extinct, seemingly because they had been outcompeted, the scientists thought.

But when Lenski and his team replayed evolution, reviving samples stored before the non-citrate eaters vanished, these bacteria survived 40 out of 40 times in a mixed population. An unknown lab accident probably finished them off the first time around, the team concluded this year (SN: 9/19/15, p. 11). Unlike in the real world, these bacteria are getting another shot at survival. A 13th flask has been added to the experiment.

Tina Hesman Saey is the senior staff writer and reports on molecular biology. She has a Ph.D. in molecular genetics from Washington University in St. Louis and a master’s degree in science journalism from Boston University.

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