Posted on 05/18/2006 11:16:00 AM PDT by PatrickHenry
Forcing Darwin's hand: capturing natural selection in a flask
Even with modern genomic tools, it's a daunting task to find a smoking gun for Darwinian evolution. The problem lies in being able to say not just when and how a specific gene mutated but also how that one genetic change translated into real-world dominance of one population over another.
Rice University biologists, using an ingenious experiment that forced bacteria to compete in a head-to-head contest for evolutionary dominance, today offer the first glimpse of how individual genetic-level adaptations play out as Darwinian natural selection in large populations. The results appear in the May 19 issue of Molecular Cell.
"One of our most surprising findings is that an estimated 20 million point mutations gave rise to just six populations that were capable of vying for dominance," said lead researcher Yousif Shamoo, associate professor of biochemistry and cell biology. "This suggests that very few molecular pathways are available for a specific molecular response, and it points to the intriguing possibility of developing a system to predict the specific mutations that pathogens will use in order to become resistant to antibiotics."
Rice's study involved the heat-loving bacteria G. stearothermophilus, which thrives at up to 73 degrees Celsius (163 F). Shamoo and graduate students Rafael Couñago and undergraduate Stephen Chen used a mutant strain of the microbe that was unable to make a key protein that the bacteria needed to regulate its metabolism at high temperatures. They grew the bacteria for one month in fermentor, raising the temperature a half degree Celsius each day.
Over a span of 1,500 generations, the percentage of mutant strains inside the fermentor ebbed and flowed as the single-celled microbes competed for dominance. Eventually, one strain squeezed out almost all the competition by virtue of its ability to most efficiently metabolize food at high temperature.
The metabolic protein required to thrive at high-temperature could only be made in one genetic region of the bacteria's DNA, meaning the researchers had only to characterize that small region of the genome for each new strain in order to measure evolutionary progress.
The researchers sampled the fermentor for new strains every other day. Though millions of mutations in the target gene are believed to have occurred, only about 700 of those were capable of creating a new variant of the target gene. In all, the researchers identified 343 unique strains, each of which contained one of just six variants of the critical gene.
The first of the six, dubbed Q199R, arose almost immediately, and was the dominant strain through the 500 th generation. Around 62 degrees Celsius, the Q199R was unable to further cope with the rising temperature, and a new round of mutations occurred. Five new varieties - themselves mutant forms of Q199R - vied for final domination of the fermentor. Three of the five were driven to extinction within a couple of days, and the final two fought it out over the remaining three weeks of the test.
The research included a raft of additional experiments as well. The team characterized each of the mutant proteins to document precisely how it aided in metabolic regulation. The fermentor experiment was repeated and the same mutations - and no others - were observed to develop again. Three of the six genes - the "winner," it's closest competitor and Q199R - were spliced back into the original form of the bacteria and studied, to rule out the possibility that mutations in other genes were responsible for the competitive advantage.
Shamoo said it's significant that the mutations didn't arise where expected within the gene. Four of the six occurred in regions of the gene that are identical in both heat-resistant and non-heat-resistant forms of G. stearothermophilus . Shamoo said this strongly shows the dynamic nature of evolution at the molecular and atomic level.
Shamoo said the most promising finding is the fact that the follow-up test produced precisely the same mutant genes.
"The duplicate study suggests that the pathways of molecular adaptation are reproducible and not highly variable under identical conditions," Shamoo said.
The research was funded by the National Science Foundation, the Welch Foundation and the Keck Center for Computational and Structural Biology.
You thought otherwise?
You apparently are misunderstanding the purpose of this, I'll explain later. My wife is calling me :-)
Cheers!
Probably the words *estimated* and *are believed*. The use of them does not imply that there is much more solid information like the words *measured* or *counted* would.
What are the units on the 17+/-2, 29+/2, etc., please?
Cheers!
"Reality" is nothing but what the evilution conspiracy makes you want, nay NEED, to believe! (Muhwahahahahahahaha!!)
No statement or disclosure in the preceding message is intended to deny or detract from the fact that reality is also and further determined by other affiliates of the Global Amalgam of Conspiracies and Nefarious Schemes, including, but not limited to, the Round Earth Conspiracy, The Non-Hollow Earth Conspiracy, and The Earth Not-Created-Last-Thursday Conspiracy. Various terms and conditions may apply.
Do not meddle in the affairs of dragons,
for you are crunchy and go well with ketchup.
Cheers!
Not quite fair comparison there, RWP, since they designed things so that by FAR the largest selection pressure was for one environmental condition only. Therefore the small population size, smaller number of mutations would not necessarily be as important as "in the wild" (where there are *many* things which must be adapted to).
BTW interesting question that brings up. Were the beneficial mutations here actually *point* mutations or the results of several mutations at widely spaced locations, happening in just the right combination? I don't recall seeing.
Cheers!
<< Did the same number happen in the same locii in both iterations? >>
And this, Latin students -- "locii" -- is what we call a plural of a plural -- a "superplural."
I often see computer geeks online using the non-word "virii" to refer to the plural form or "virus" -- but this is the first "locii" I have ever seen. I love it.
But now that I think of it -- this could be referring to multiple clones of the Vikings' trickster god.
Just teasing ya, jwalsh -- I am a Latin teacher and I get a kick out of these things, the same way computer geeks get a laugh out of my mangling of tech-talk.
Just the man I've been looking for! How would you render the slogan of Darwin Central (the conspiracy that cares) into Latin? The best w've come up with are the following:
1. Coniuratio habita clementiam. "The conspiracy having compassion"
2. Coniuratio quae sollicita est. "The conspiracy which is concerned."
3. Coniuratio Alma "The nourishing (or kind) conspiracy."
4. Coniuratio Compatiens "The caring conspiracy."
5. Coniuratio quae patitur. "The conspiracy that suffers (or experiences, bears, tolerates, endures, allows)."
6. Coniuratio quae compatitur. "The conspiracy that has compassion (or feels pity, suffers with one)."
7. Coniuratio quae compatitur dolorem tuum. "The conspiracy that feels your pain."
<< Before Newton, angels were pushing the planets around. >>
Back in Newton's time, he was roundly criticized by religious folks for making science atheistic -- and if he had revealed his rejection of the Trinity, he could have lost his job and his reputation. Today, creationists like to use him as evidence of creationism, because, don't you see, he believed in God and in divine design.
In fact, we even had one recently in here who was using Pythagoras -- PYTHAGORAS -- for the same purpose! I guess that means we should avoid beans and never poke a fire with a stick, which Pythagoras's cult also taught. LOL!
<< Yes, the God of the Gaps effect has also shrunk the angels. :-( >>
Heisenberg angels!
<< There weren't two living things put together to fight it out. There was a single strain of bacteria. Over time, mutation caused new strains to evolve. At one point, there were 6 vying for dominance. One finally came dominate all the rest. >>
Attila the Germ.
<< Aren't these attacks a little beneath you? >>
Yes, these attacks are WAY beneath PH, and that is why I am convinced I will never see PH engage in such things. They are exactly the attacks we see and hear constantly from creationists in myriad crevo discussions all over the net, including in here.
PH was doing nothing but quoting his opponents.
Before Newton the Cartesian mechanistic model of gravity prevailed. The main criticism of Newton came from rationalists like Leibniz who made the entirely reasonable criticism that his model of gravity constituted "action at a distance." Leibniz's point was that Newton's model was in effect positing a miracle-- hardly an argument that it had "made science atheistic."
What has selection pressure to do with the point mutation rate?
No problem, I can take the teasing. But what makes you think it wasn't a tyypo?
Now a question for you.
Is there only one solution set for this temperature increase?
100
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