Science: A New Step In Evolution

• Views: 1,570

Carl Zimmer has a fascinating post at The Loom (part of the ScienceBlogs network), with more details on that 20-year experiment in evolution conducted by Richard Lenski at Michigan State University: A New Step In Evolution.

Based on what scientists already knew about evolution, Lenski expected that the bacteria would experience natural selection in their new environment. In each generation, some of the microbes would mutate. Most of the mutations would be harmful, killing the bacteria or making them grow more slowly. Others would be beneficial allowing them to breed faster in their new environment. They would gradually dominate the population, only to be replaced when a new mutation arose to produce an even fitter sort of microbe.

Lenski used a simple but elegant method to find out if this would happen. He froze some of the original bacteria in each line, and then froze bacteria every 500 generations. Whenever he was so inclined, he could go back into this fossil record and thaw out some bacteria, bringing them back to life. By putting the newest bacteria in his lines in a flask along with their ancestors, for example, he could compare how well the bacteria had adapted to the environment he had created.

Over the generations, in fits and starts, the bacteria did indeed evolve into faster breeders. The bacteria in the flasks today breed 75% faster on average than their original ancestor. Lenski and his colleagues have pinpointed some of the genes that have evolved along the way; in some cases, for example, the same gene has changed in almost every line, but it has mutated in a different spot in each case. Lenski and his colleagues have also shown how natural selection has demanded trade-offs from the bacteria; while they grow faster on a meager diet of glucose, they’ve gotten worse at feeding on some other kinds of sugars.

Last year Lenski was elected to the National Academy of Sciences. This week he is publishing an inaugural paper in the Proceedings of the National Academy of Sciences with his student Zachary Blount and postdoc Christina Borland. Lenski told me about the discovery behind the paper when I first met him a few years ago. He was clearly excited, but he wasn’t ready to go public. There were still a lot of tests to run to understand exactly what had happened to the bacteria.

Now they’re sure. Out of the blue, their bacteria had abandoned Lenski’s their glucose-only diet and had evolved a new way to eat.

After 33,127 generations Lenski and his students noticed something strange in one of the colonies. The flask started to turn cloudy. This happens sometimes when contaminating bacteria slip into a flask and start feeding on a compound in the broth known as citrate. Citrate is made up of carbon, hydrogen, and oxygen; it’s essentially the same as the citric acid that makes lemons tart. Our own cells produce citrate in the long chain of chemical reactions that lets us draw energy from food. Many species of bacteria can eat citrate, but in an oxygen-rich environment like Lenski’s lab, E. coli can’t. The problem is that the bacteria can’t pull the molecule in through their membranes. In fact, their failure has long been one of the defining hallmarks of E. coli as a species.

If citrate-eating bacteria invade the flasks, however, they can feast on the abundant citrate, and their exploding population turns the flask cloudy. This has only happened rarely in Lenski’s experiment, and when it does, he and his colleagues throw out the flask and start the line again from its most recently frozen ancestors.

But in one remarkable case, however, they discovered that a flask had turned cloudy without any contamination. It was E. coli chowing down on the citrate. The researchers found that when they put the bacteria in pure citrate, the microbes could thrive on it as their sole source of carbon.

In nature, there have been a few reports of E. coli that can feed on citrate. But these oddballs all acquired a ring of DNA called a plasmid from some other species of bacteria. Lenski selected a strain of E. coli for his experiments that doesn’t have any plasmids, there were no other bacteria in the experiment, and the evolved bacteria remain plasmid-free. So the only explanation was that this one line of E. coli had evolved the ability to eat citrate on its own.

Read the whole thing…

Jump to top

Create a PageThis is the LGF Pages posting bookmarklet. To use it, drag this button to your browser's bookmark bar, and title it 'LGF Pages' (or whatever you like). Then browse to a site you want to post, select some text on the page to use for a quote, click the bookmarklet, and the Pages posting window will appear with the title, text, and any embedded video or audio files already filled in, ready to go.
Or... you can just click this button to open the Pages posting window right away.
Last updated: 2016-01-01 10:29 am PST
LGF User's Guide RSS Feeds Tweet

Help support Little Green Footballs!

Subscribe now for ad-free access!Register and sign in to a free LGF account before subscribing, and your ad-free access will be automatically enabled.

Donate with
PayPal
Square Cash Shop at amazon
as an LGF Associate!
Recent PagesClick to refresh
McCain Associate Invokes Fifth Amendment on Trump Dossier Sources: Report An associate of Sen. John McCainJohn Sidney McCainLawmakers worry about rise of fake video technology Democrats put Dreamers and their party in danger by playing hardball Trump set a good defense budget, but here is how to make it ...
Thanos
7 hours, 35 minutes ago
Views: 97 • Comments: 0 • Rating: 0
Tweets: 0 • Share to Facebook
Shares: 0
Comments: 0
: 0
Live From Daryl’s House - ‘I’m Alright’On this episode of Live From Daryl's House, Kenny Loggins drops by to get "Footloose" with Daryl and his band.
Thanos
1 day, 8 hours ago
Views: 151 • Comments: 0 • Rating: 1
Tweets: 0 • Share to Facebook
Shares: 0
Comments: 0
: 0
Author Retraces Her Journey From Survivalist Childhood to Cambridge Ph.D. As a girl, Westover says, "There wasn't ever any question about what my future would look like: I would get married when I was 17 or 18, and I would be given some corner of the farm and my ...
Thanos
1 day, 22 hours ago
Views: 235 • Comments: 2 • Rating: 5
Tweets: 1 • Share to Facebook
Shares: 0
Comments: 0
: 0
Florida Republicans Choose Unregulated Murder Weapons Over Children’s LivesI keep drilling this to everyone who discusses this shooting. Republicans value ownership of unregulated murder weapons over children's lives. So much so that they voted along party lines with Stoneman Douglas students watching they voted to decline debate on ...
TDG2112
2 days, 6 hours ago
Views: 261 • Comments: 0 • Rating: 0
Tweets: 0 • Share to Facebook
Shares: 0
Comments: 0
: 0
Weekend Box Office: ‘Black Panther’ Bounds to Record-Shattering $218M-Plus Bow In a defining moment for Hollywood, Disney and Marvel Studios' Black Panther exploded at the Presidents Day box office, bounding to a record-shattering estimate of $192 million for the three-day weekend and a projected $218 million-plus for the four-day ...
Thanos
4 days, 12 hours ago
Views: 509 • Comments: 0 • Rating: 1
Tweets: 0 • Share to Facebook
Shares: 0
Comments: 0
: 0
Brandi Carlile - the Joke (Official Video) From the album "By The Way, I Forgive You" available now. elektrar.ec Directed by Danny Clinch Produced by Lindha Narvaez for MILKT Choreography by Peter Leung Ballet sequence filmed by Middle Table Productions Connect with Brandi: brandicarlile.com facebook.com @brandicarlile ...
Thanos
5 days, 8 hours ago
Views: 552 • Comments: 0 • Rating: 1
Tweets: 0 • Share to Facebook
Shares: 0
Comments: 0
: 0
School Shooter Nikolas Cruz Belonged to White Supremacist GroupThis my surprised face.... BREAKING: Nikolas Cruz, alleged perpetrator in the deadly school shooting in Parkland, Florida, was associated with white supremacist group Republic of Florida & participated in the group’s training exercises, according to the group’s leader. More info: ...
Scottish Dragon
1 week ago
Views: 694 • Comments: 2 • Rating: 1
Tweets: 0 • Share to Facebook
Shares: 0
Comments: 0
: 0
Your Medicine Cabinet Knows What AIls Youblog.timesunion.com HOFFMAN FILESYour medicine cabinet knows what ails you.By Rob Hoffman on February 15, 2018 at 5:27 AM1We all fancy ourselves experts when it comes to the human condition. We see our fellow human beings as open books, and we ...
rhoffman
1 week ago
Views: 675 • Comments: 0 • Rating: 0
Tweets: 0 • Share to Facebook
Shares: 1
Comments: 0
: 1
A.G. Schneiderman Files Civil Rights Lawsuit Against the Weinstein Companies, Harvey Weinstein, and Robert Weinstein NEW YORK – New York Attorney General Eric T. Schneiderman today filed suit against The Weinstein Company (“TWC”), Harvey Weinstein, and Robert Weinstein for egregious violations of New York’s civil rights, human rights, and business laws. The suit, filed ...
Thanos
1 week, 4 days ago
Views: 1,422 • Comments: 0 • Rating: 1
Tweets: 5 • Share to Facebook
Shares: 2
Comments: 0
: 2
Portugal. The Man - Keep on (Official Video) Portugal. The Man - Keep On Video conceptualized, created and directed by Paulin RoguesFollow Paulin at instagram.com Catch Portugal. The Man on tour:portugaltheman.com WOODSTOCK available now!atlantic.lnk.to Follow Portugal. The ManWebsite: portugaltheman.comFB: facebook.com IG: instagram.comTW: @portugalthemanSC: SoundCloudYT: youtube.comTumblr: portugaltheman.tumblr.com ...
Thanos
1 week, 5 days ago
Views: 1,524 • Comments: 0 • Rating: 0
Tweets: 1 • Share to Facebook
Shares: 0
Comments: 0
: 0