Science

The evolution experiment that has been watching bacteria mutate for 30 years

The evolution experiment that ...
The experiment has observed more than 67,000 generations of bacteria, equivalent to one million years of human evolution
The experiment has observed more than 67,000 generations of bacteria, equivalent to one million years of human evolution
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Mike McDonald, a recent ARC Future Fellow with Laura Woods (left) and Aysha Sezmis (right)
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Mike McDonald, a recent ARC Future Fellow with Laura Woods (left) and Aysha Sezmis (right)
The experiment has observed more than 67,000 generations of bacteria, equivalent to one million years of human evolution
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The experiment has observed more than 67,000 generations of bacteria, equivalent to one million years of human evolution

Thirty years ago the world's longest running evolution experiment began when scientist Richard Lenski seeded 12 identical flasks with E. coli bacteria. Every subsequent day someone in the lab has transferred a sample of each flask into a new flask and every 75 days a sample is frozen acting like an evolutionary time capsule.

After three decades the experiment has rolled through more than 67,000 generations of E. coli, which the researchers note is equivalent to over one million years of human evolution.

"Our study, published in Nature, provides a high-resolution view of the molecular details of adaptation over substantial evolutionary timescales," says study co-lead author Dr Mike McDonald.

"The insights we provide into the rate, repeatability, and molecular basis of adaptation will contribute to a better understanding of these evolutionary processes and challenges."

One of the most compelling results of the experiment has been the observation that the bacteria has seemingly been constantly evolving despite the static, and unchanging, simplicity of its environment.

"In our study we found that even though the E. coli populations in our experiment have been evolving in a very simple environment for a long time, they are still adapting to their environment," says Dr McDonald.

"In other words the fit get fitter. But the established theory tells us that adaptation should have stopped by now since there should be a 'fitness peak' that the E.coli should have reached by now – and our work shows that this is not the case."

The researchers hypothesize that the constantly evolving E. coli is dynamically changing the environment it is growing in. This results in a kind of feedback loop where the bacteria evolve and change its environment, stimulating yet another stage of evolution. Thus, despite a static environment, the population should never stop evolving.

Mike McDonald, a recent ARC Future Fellow with Laura Woods (left) and Aysha Sezmis (right)
Mike McDonald, a recent ARC Future Fellow with Laura Woods (left) and Aysha Sezmis (right)

Unsurprisingly, all 12 bacterial cultures have improved in competitive fitness over the thirty year evolution. They all grow faster and have bigger cells than at the start of the experiment, but each culture has developed its own unique pathway to better fitness.

Perhaps the most novel evolutionary tweak arose in one of the cultures at about 20,000 generations. A culture evolved the ability to eat citrate in addition to glucose, a feature not previously seen in E. coli bacteria.

McDonald sees this ongoing experiment in evolution as offering a vital understanding into how we can better predict the adaptive changes that result from evolutionary processes.

"Cancer is an evolving group of cells within your body, antibiotic resistance is the result of bacteria adapting to the use of antibiotics, and climate change is forcing whole ecosystems to adapt or die," says Dr McDonald.

There are no plans to end the E. coli experiment any time soon, with scientists continuing to reset the flasks every day and observe the ongoing evolution of the Lenski bacteria.

The latest study was published in the journal Nature.

Source: Monash University

7 comments
Bob
They adapt to survive BUT they are still E, coli bacteria. They did not evolve into anything else nor become more complex.
John Kline Kurtz
...Or perhaps the bacteria are "preprogrammed" with the ability to adjust to the environment in ways that surprised these researchers. They are still bacteria and not slugs or clams.
Cody Blank
Bob they did become more complex, one of them evolved the ability to eat a food no other ecoli ever has.
Pupp1
These bacteria always had the ability to metabolize citrate. However, they normally have a cell wall that will keep the citrate on the inside of their cell wall. Thus, they can't get it from their environment.
But, rather than evolving any new genetic information, it might be better described as a devolution in the cell wall.
An good analogy might be a cat that is stuck in a house with all the windows closed. A storm knocks a tree over, that breaks a skylight. Thus, the house "evolved" the ability to feed the cat, because it broke.
To stay with the same analogy, true evolution would be something like when winter comes and it gets cold, a lighting strike melts some sand by the same house, and then a tornado comes along and somehow forms a new window to replace the broken one. Thus the cat can keep warm. But obviously, the odds are this happening are so extremely remote, as to be ridiculous.
Bob
Sorry Cody but they are STILL E.coli and simply adapted to a new food source. If you want this experiment to prove evolution then the bacteria need to change into something else like another strain of bacteria or even a one celled animal. Anything that isn't still an E. coli. If anything, this proves evolution does not exist.
John Kline Kurtz
An excellent article for further consideration on this subject is at: icr.org/article/10189 and is titled "Engineered Adaptability: Adaptability via Nature or Design? What Evolutionists Say"
TechGazer
The experiment is still a short time in terms of evolution, and extremely limited in its environment and size. Bacteria didn't become something more advanced until one swallowed a different species which later evolved into mitochondria, providing the energy required to support more advanced life. To prove evolution the way Bob seems to expect would probably require an entire world and a billion years or so. It worked on our world, so that seems to prove that evolution does occur. Doing it on another world (and a long period of time) would just be the duplication phase of the experiment.