I would like to read the primary research article. However this is intriguing. Bacteria have the ability to share and uptake plasmid DNA that codes for certain genes that allow them to preform different functions. I don't really find it plausible that their current genome somehow mutated and gave them the ability to metabolize citrate as much as I believe one of the E. coli bacteria had the ability to metabolize citrate and that bacterium reproduced while those that could not metabolize citrate died off.
First of all, Digs, I am very impressed with your knowledge, and I think it's awesome that you are studying biology. It's a very rewarding field, even though it's hard work at times, and I wish you the best of luck in whatever avenue you take.
That being said, let me just clear up a few things. The first issue is the ability (or rather, the lack thereof) to metabolize citrate by
E.coli. As i'm sure you're aware,
E coli is unable to metabolize citrate; in fact, that's one of the distinguishishing factors to identify the bacteria as
E. coli. Lenski's bacteria were no different back in 1988, when he began the experiment. None of the bacteria could metabolize citrate (just like any other
E.coli), and the glory of Lenski's experiment is that clonal representatives were stored frozen from time to time, so all he had to do was thaw them out to collect any data he needed about earlier generations. This means that he is able to do any other experiments with 'earlier models' that he has need to, and he can detect the various generational mutations that have sprung up. So, if anyone had any questions about earlier generations, he can answer them by simply thawing out a few samples.
Also, you brought up plasmids. Good question - how do we know some piece of random genetic material from some other organism didn't find it's way into Lenski's bacteria and let them start consuming citrate? As it turns out, Lenski's bacteria are strictly asexual. But unlike other bacteria, which are also asexual, but can engage in sexual processes to transfer genetic material, Lenski's bacteria lacked the potential to do this. But even if they could, plasmid DNA (or any other exogenous DNA) can only be taken up by a a cell if it is competent, and of course, there has to be exogenous DNA around. Lenski's clones were kept free from contaminates, and any samples that ended up contaminated were tossed, and the latest generational samples unfrozen and allowed to continue reproducing. Thus, there would be no plasmids nor any other exogenous DNA in his clones for transformation to actually take place, even if Lenski's bacteria were somehow able to do so.
Your concern was also over the mutations. As you know from your studies in molecular genetics, there are plenty of mutations that take place in our own DNA over time - some are point mutations, others can be larger changes on a molecular level, and even others can be large chromosomal changes. Very few of these actually make it to the next generation, and Lenski's bacteria is no exception. The repair mechanisms are very efficient, so most of the errors are corrected before replication begins. However, Lenski noticed that some of his bacteria over time had developed mutations that did, in fact, make it through to the next generation. Some of the bacteria had problems growing on D-ribose. Cell volume increased. And of course, there is the appearance citrate metabolising generations. What exact genomic changes took place I cannot say, as I have not revisited Lenski's study in quite a while. However, given the lack of any contaminants, exogenous DNA, and the ability to replicate this by thawing earlier generations of Lenski's
E.coli, what he has shown is Evolution in action, and on a scale where it is easily witnessed within a reasonable time frame. And the glory of the entire experiment is that it is totally reproducible. If someone doubts that the bacteria can't do it again, all Lenski has to do is thaw an earlier generation.
This is no surprise to any biologist, as there is overwhelming evidence that Evolution takes place not only on a genetic level, but phenotypically. For all it's apparent randomness, from a biological perspective, things in nature are actually quite organized. Living creatures have adapted behaviorally and morphologically to the environments in which they are found, and it's easy to see why some folks can take this as being designed from a creator. Evolutionary biology, however, easily demonstrates that this is not the case. While a creator may have 'started the process' so to speak, every life form we see today evolved from a previous ancestor.
I think it would be an example of natural selection, however I would like to read the primary research article to examine their methods and discussion section. I don't discount the fact that single celled organisms can evolve (microevolution), but I am extremely skeptical of macroevolution (speciation, etc.)
The article is readily available online if you wish to browse through it. I also have a copy from a few years ago that I could PM you if you want to read the experiment.
