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.
Creationist: Evolution isn't science. It can't be duplicated in a lab.
Scientist: Yes it can! Here's an example of how evolution can be duplicated in an exactly reproducible way.
Creationist: But you did it in a lab. You designed the experiment, so it isn't evolution!
Repeat until the scientist becomes nauseous.
More importantly, this experiment refutes the creationist canard that evolution is a random process.
That's geek-speak for "evolution is testable."
So you say, monkey-boy! Meanwhile, creationist research is moving along very nicely: NoahsArkSearch.
But they're still microbes.
It is those macrobes you need to look out for. Big enough to trip over.
Estimate based upon known rates.
The conclusion reached by the researchers seems to be that " "The duplicate study suggests that the pathways of molecular adaptation are reproducible and not highly variable under identical conditions," Shamoo said.
Why?
Proteins will not have an infinite number of useful sequences at any particular set of conditions. Many of the point mutations that occurred will not have caused any change in the protein sequence due to codon redundancy. Other point mutations will cause sequence change that is neutral and likely to be lost through genetic drift. Others will cause sequence change that is detrimental. They found the few beneficial point mutations that make the protein more effective under the specific conditions tested.
It is like when you get in your car to drive to work there are hundreds of routes you could take, but probably only a couple that get you there in good time.
Before Newton, angels were pushing the planets around. Now they lurk in cells and rearrange DNA.
Yes, the God of the Gaps effect has also shrunk the angels. :-(
So, in other words, this experiment managed to 'capture' the Intelligent Designer in a bottle and made it do it's design work over and over again? Do you realize that in your post, you are implying that science tested God's creative ability in a test tube and controlled it? The other option is that is was the product of natural causes.
You forgot to mention that if the experiment is reproducible, it isn't random.
Just being helpful.
You're not reading the article correctly.
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.
This stain was not part of the original culture. It evolved.
It depends on the temperature, since G. stearothermophilus RNA denatures with an increase in heat. At 20oC, A-U is 17+/-2 and G-C is 29+/-2. At 52oC, A-U is 7+/-2 and G-C is 25+/-2.
What is the mutation rate per generation?
0.4% (1 base in 250 mutated) per generation.
How many bases were impervious to mutation?
8+/-3.
At least one of the above answers is correct and at least one is incorrect. Please identify and correct any wrong answers.
No fair. You've played this game before.
This is exactly the kind of experiment that creationists said had to be done to prove evolution could happen. They're identifying the exact genes that mutate, what they mutate to, the proteins that are formed, the pathways that they affect in the cell metabolism, and they're able to replicate it.
Do I see the bar raising again?
And isn't it great that creationists don't have to do any work to create evidence for their ideas?
How many base pairs in the target gene?
1953
What is the mutation rate per generation?
Approximately 5 X 10-10 per nucleotide per generation
How many bases were impervious to mutation?
None. There were 5 X 1010 cells in the turbidostat. That means that there were, on average, 25 mutants for each base pair present in the turbidostat. The system was mutationally saturated, and so probed all possible single-point mutational selection paths.
Done this kind of thing many times although without the genetic tools in some cases.
Did you sneak into the lab at midnight to do your cackling like I did?
No, I cackled openly, in between saying things like, "Yuck, this stinks."
Lies ... frauds ... Hitler ... it's all about sex ... atheism ... government grants ... leftists ... evil ...
</whimpering creationist mode>
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