Tuesday, April 6, 2010

Bacteria: A Gift to Science or a Curse?

Bacteria have the ability to adapt to new environments relatively rapidly because adaptations occur over many generations, but some bacteria replicate as often as every 20 minutes. As a result, within just a few days, bacteria can go through hundreds, if not thousands, of generations. This makes them prime candidates to undergo lab simulated evolution to help us get a better understanding of evolution and survival. On page 128, Coyne describes how bacteria can quickly adapt to simple hazardous environments. Quite surprisingly, he also goes on to show how they can adapt to more complex situations in the example of Barry Hall's experiment with E. coli and lactose. Explain Dr. Hall's experiment and why it is so significant in the debate of evolution versus intelligent design. Provide another example of a species which was introduced into a similar situation and modified its current genes to survive. However, this rapid adaptation to bacteria has costly effects such as their rapid immunization to antibiotics. Expand Coyne's statement of simple adaptations of bacteria in labs to explain how bacteria become immune. Give an example of a bacteria that, through adaptations, has become immune. Does the benefit of medicine outweigh the threat of evolving a more deadly bacteria?


  1. In Dr. Hall’s experiment, he wanted to figure out if a microbe, like E. coli, can work around a problem its facing. By deleting a gene in the E. coli, he deleted an enzyme that put it at the disadvantage of not being able to break down lactose for food. After the gene was deleted the E. coli was then put into an environment where it was surrounded by lactose, unable break it down and obtain its nutrients. Unable to eat, it was unable to grow. After a period of time though, “the function of the missing gene was taken over by another enzyme”, which could break down lactose but at a slower pace. This by itself is greatly significant as it shows the E. coli was modifying features it already had in order to adapt to this new situation. The process was slow, but that also demonstrates that evolution isn’t immediate. As time went on the enzyme the E. coli had did not increase in speed, but in amount. With more enzyme, even at the slow pace, it could break down lactose faster so than it had before. When it comes down to evolution versus intelligent design, intelligent design proposed that natural selection couldn’t encourage the evolution of biological systems when they are supposed to be codependent. After this experiment where the E. coli got over a very complex problem, that statement was proven false.

    A similar situation would be how Richard Lenski put E. coli in an environment where their food was depleted each day and then renewed the next. This gave the E. coli a change to eat as much as it wanted before being forced to starve. These conditions weren’t usual for the E. coli and after running this experiment for 18 years the E coli were able to grow, “70 percent faster than the original unselected strain,” Like the E. coli in Hall’s experiment, the microbe modified itself in order to survive after many generations.

    Bacteria become immune to antibiotics by modifying themselves and mutating over generations in order to fight off antibiotics attacks. This can be in the form of preventing an antibiotic from getting to its target by changing the permeability of their membranes, another is changing their target by no longer allowing the antibiotic to recognize it and identify it as the enemy, and last destroying the antibiotic by sometimes creating enzymes to use against it (How Stuff Works). This again, happens over a long period of time, as the bacteria get acquired resistance by “getting a copy of a gene encoding an altered protein or enzyme” (How Stuff Works).

    A resistant bacteria would be Staphylococcus aureus, which is 95% resistant too pencillin and 60% resistant too methicillin worldwide. It’s known for causing food poisoning, toxic shock syndrome, and skin infections (Actionbioscience). Medicine still plays a huge role in curing a whole spectrum of diseases, but in order to avoid a superbug we would have to try and discover different therapies. One possibly could be bacteriophage therapy that is more specific then a common drug and harmless to the human host. (Wikipedia)

    Book (pgs 128-129(

  2. As the response above has already delineated Dr. Hall's experiment, I will not belabor the details of the experiment itself, but rather the conclusions and ramifications of the results found. We see in the Hall experiment that evolution does have the capacity to result in complex, interconnected biochemical systems. That is, the framework of chemical processes centered around an organism's ability to survive may develop from what appears to be a very small set of instructions (genes) even in low-level organisms. In the case of the Hall experiment, the process studied was the ability to break down lactose, which would usually be taken care of with a gene that causes production of an enzyme to carry out the process; however, having the gene that enables the bacteria to break down its only source of nutrition snipped out would, at first thought, seem as if it would result in the immediate death of the entire colony subject to these pressures. It is shown that after simple gene mutations, these bacteria do slowly activate another pathway to make their source of nutrition usable. It is unlikely that bacteria would be able to suddenly change their mode of nutrition, but mutations that change enzymes slightly (perhaps changing their active sites to 'sort-of' fit lactose for its breakdown) are quite possible, especially given the fact that bacteria reproduce quickly and many generations result over a short period of time. As our textbook says on page 154, enzymes may adjust their active sites to change shape slightly so that the substrate may fit “more snugly”, in this induced fit model.

    Of course, all of this relies on the fact that evolution of bacteria and other microbes is indeed evolution. Coyne states on page 128 that this is indeed “genuine evolutionary change” due to the fact that it satisfies the three criteria for evolution caused by natural selection (it is important to note this definition, which creationists may have a difficult time arguing against), that is “variation, heritability, and the differential survival and reproduction of variants.”

    As for antibacterial resistance, these disease causing microbes have chance mutations that allow them to survive to reproduce despite the antibacterial agents we put out in an attempt to defend ourselves against disease. This is seen in the bacteria Mycobacterium tuberculosis (italicized), the bacterium which is the cause for tuberculosis, whose resistance to antibiotics has become a grave issue and danger to those afflicted. A key adaptation for its resistance may likely be its cell wall comprised of an unusually high amount of long fatty acids, or lipids as well as modifications to the cell wall which allow for heightened response to even rapidly changing environmental stimuli (Wikipedia). While some would argue that it may be a part of natural selection and evolution for those humans who succumb to the bacterium to die, allowing other humans who have resistance to pass on their favorable genes to the next generation, a moral argument may come into play (one which I will not even begin to address). Medicine does, however, prevent and/or treat disease among members of our species, and invariably, bacteria, like any other organism, will continue to evolve, adapting to changing times and environments in an attempt to survive and reproduce (do not take this to mean that the goal of evolution is to change, a misconception that Coyne has tried to clear, and one into which I do not intend to fall).