Thirty years ago, Michigan State University researcher Richard Lenski added his now-famous bacteria to 12 inaugural flasks, a process he and his team of lab technicians and students have been repeating daily ever since.
Through the years—and more than 68,000 generations of bacteria later—the experiment also has earned the MSU Hannah Distinguished Professor of Microbiology and Molecular Genetics multiple accolades, including the title “The Man Who Bottled Evolution” by the likes of Science magazine.
But who, outside of the science community, should care about this milestone? Why celebrate and why bacteria?
Because the LTEE shows how seemingly small mutations lay the groundwork for evolution. Lenski’s bacteria grow more than six generations a day. It takes mice a year to do the same thing. On human terms, the LTEE generations span the equivalent of well more than a million years of human evolution.
The long-term experiment demonstrates definitively—rather than theoretically—how new lineages arise and diverge. It confirms that evolution occurs, is ever-present and never stops. In other words, according to science writer Carl Zimmer, Lenski has done something Darwin never dreamed of: he has observed evolution in his own time.
Few scientists actually proclaim “Eureka” when making a major discovery. This was the case in 2003 when Lenski and his students noticed one of the 12 LTEE flasks looking quite different from the others. Their “eureka moment” began, instead, with thinking the flask was contaminated.
Here’s where it got interesting. The LTEE is special because it allows the team to “replay” evolution and thereby probe the effects of prior history on later events. After every 75 days (500 generations), the bacteria are frozen. This serves as an organic data backup of sorts, allowing scientists to thaw and revive living “fossils.” They use this procedure routinely to have the ancestors compete against their many-thousands-of-generations-later descendants.
In the 2003 case, by restarting the questionable culture and observing the same unexpected results, the scientists identified the cause as adaptation rather than contamination; the bacteria had evolved to eat something other than glucose—standard fare for all the other generations of their bacteria.
The team also was able to pinpoint genetically how and where it happened.
These special bacteria had begun consuming citrate, a compound found in citrus fruits that also was present, all along, as part of the culture medium used to grow the E. coli in the LTEE.
“I like to say that the bacteria would eat dinner every night without realizing there was this nice, lemony dessert right around the corner,” Lenski says. Thirty years and counting, still only one of the 12 populations has figured it out and ordered dessert.
The long-term experiment can contribute to medical advances. It has inspired many studies—in the lab, in the clinic and in nature—to better understand the evolution of pathogenic bacteria, fungi and viruses.
For example, this winter looks to become one of the worst flu seasons in the past decade, and there have been recent concerns about avian and swine flu. How can scientists better understand how strains pass from animals to humans? How can doctors see a common flu virus give rise to a deadly epidemic? You guessed it: evolution.
Besides his work on the LTEE, other research co-led by Lenski showed how viruses evolve complex and potentially deadly new traits—a process that took the featured virus merely four mutations to accomplish. Luckily, in this case, the virus is one that infects bacteria, not humans.
Such insights can lead to new ways to understand, prevent and perhaps better treat diseases.
Lenski, a founding member of the BEACON Center for the Study of Evolution in Action at MSU, hopes his experiment outlives his tenure. Before he retires, he’d like to establish an endowment to keep the experiment going in perpetuity.
“I call this the experiment that keeps on giving,” Lenski says. “Even after 30 years, it’s still generating new and exciting discoveries. From models, we can predict how things will evolve—how fit the bacteria will become—if future generations of scientists continue the experiment long after I’m gone.”