Bacteria make major evolutionary shift in the lab

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A major evolutionary innovation has unfurled right in front of researchers' eyes. It's the first time evolution has been caught in the act of making such a rare and complex new trait.

And because the species in question is a bacterium, scientists have been able to replay history to show how this evolutionary novelty grew from the accumulation of unpredictable, chance events.

Twenty years ago, evolutionary biologist Richard Lenski of Michigan State University in East Lansing, US, took a single Escherichia coli bacterium and used its descendants to found 12 laboratory populations.

The 12 have been growing ever since, gradually accumulating mutations and evolving for more than 44,000 generations, while Lenski watches what happens.

Mostly, the patterns Lenski saw were similar in each separate population. All 12 evolved larger cells, for example, as well as faster growth rates on the glucose they were fed, and lower peak population densities.

But sometime around the 31,500th generation, something dramatic happened in just one of the populations – the bacteria suddenly acquired the ability to metabolise citrate, a second nutrient in their culture medium that E. coli normally cannot use.

Indeed, the inability to use citrate is one of the traits by which bacteriologists distinguish E. coli from other species. The citrate-using mutants increased in population size and diversity.

"It's the most profound change we have seen during the experiment. This was clearly something quite different for them, and it's outside what was normally considered the bounds of E. coli as a species, which makes it especially interesting," says Lenski.

By this time, Lenski calculated, enough bacterial cells had lived and died that all simple mutations must already have occurred several times over.

That meant the "citrate-plus" trait must have been something special – either it was a single mutation of an unusually improbable sort, a rare chromosome inversion, say, or else gaining the ability to use citrate required the accumulation of several mutations in sequence.

To find out which, Lenski turned to his freezer, where he had saved samples of each population every 500 generations. These allowed him to replay history from any starting point he chose, by reviving the bacteria and letting evolution "replay" again.

Would the same population evolve Cit+ again, he wondered, or would any of the 12 be equally likely to hit the jackpot?

The replays showed that even when he looked at trillions of cells, only the original population re-evolved Cit+ – and only when he started the replay from generation 20,000 or greater. Something, he concluded, must have happened around generation 20,000 that laid the groundwork for Cit+ to later evolve.

Lenski and his colleagues are now working to identify just what that earlier change was, and how it made the Cit+ mutation possible more than 10,000 generations later.

In the meantime, the experiment stands as proof that evolution does not always lead to the best possible outcome. Instead, a chance event can sometimes open evolutionary doors for one population that remain forever closed to other populations with different histories.

Lenski's experiment is also yet another poke in the eye for anti-evolutionists, notes Jerry Coyne, an evolutionary biologist at the University of Chicago. "The thing I like most is it says you can get these complex traits evolving by a combination of unlikely events," he says. "That's just what creationists say can't happen."

http://www.newscientist.com/channel/life/d...in-the-lab.html

[one...two...tree 2,762]

Very cool. Fascinating.

[almaty 19]

i agree.. nice read and informative

[HAL 9000 96]

A bunch of BS if you ask me!

J/K... awesome observations!. Some of these spontaneous mutations and up being serendipitously quite the welcome sight for many organisms that end up 'discovering' whole new sources of food.

Imagine what the pathogenic bacteria are able to dredge up as we continue to play around with population densities and environmental conditions the world over...

[Kathryn41 3,205]

Very cool article - and the experience can be readily extrapolated to other, more complex populations. Thank you.

[Mr. Big Dog 10,747]

Blasphemous Writing!

[Nessa 23]

I wish there were more threads about science and less about politics.

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I wish there were more threads about science and less about politics.

You got it, Nessa

[Ban Hammer 13,352]

we need more threads about strippers!

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charles

[Trumplestiltskin 5,791]

Bacteria make major evolutionary shift in the lab

I think its quite plausible - I mean look at some of our crazier posters

[SaadBell 0]

"That's just what creationists say can't happen."

That is very cool What do the creationists say about this

[HAL 9000 96]

Very cool article - and the experience can be readily extrapolated to other, more complex populations. Thank you.

Dunno about that... to be really plausible these complex organisms would have to have various mutations in order to metabolize new, previously unmetabolizable nutrients... bacteria have it easy being unicellular.

Hence the much longer time for evolutionary changes to become characteristic of a multicellular species or a subspecies for that matter.

Then again, time is a very relative matter in evolution. Just like in other facets of observational fields...

[Scott & Lai 12]

"That's just what creationists say can't happen."

That is very cool What do the creationists say about this

It's interesting, but not really a big deal. As a creationist (no, I don't think the Earth is just a few thousand years old...), I'm not bothered by this at all.

[one...two...tree 2,762]

Now if only some people here on VJ would evolve.