Evolution in bacteria

Written by Dr. T. M. Wassenaar Tuesday, 06 January 2009 07:32

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Like all forms of life, bacteria undergo evolution. Evolution is a slow and gradual process, and it was the person of Charles Darwin, combining keen observation with a sharp mind, who first described the principles of evolution. Had microbiology existed in those days, then he would certainly have used bacteria to illustrate his ideas. Since bacteria are relatively simple forms of life, and have a short generation time, evolutionary processes can be observed directly, as opposed to most other life forms. The study of bacterial evolution has resulted in many insights of general biological processes, and modern research still uses bacteria as a model to study evolution.

Evolution is based on three principles:

  • As organisms reproduce, more offspring will be formed than can survive. This causes competition for sources of energy and habitat. Only the fittest organisms will survive.
  • During cell division, minute changes will be introduced in the offspring. Such mutations will generate genetic diversity among the offspring.
  • The result of these two processes, competition and diversity, is a selection pressure that will favour certain populations that are best qualified to survive. Over time, this will result in notable changes of a species.


Read about this classical discovery of evolution: how bacteria could become resistant against their enemy, a bacteriophage. If you don't know what bacteriophages are, check our exhibit.
This only seems a small step on the hughe ladder of evolution, but in fact it is these small steps that over time allows the formation of new species. We observe evolution of bacteria in real time, as they divide so much faster than animals or plants. We now know that evolution is not a gradual, constant process, but rather takes place in bursts, as explained in this article on 'punk eek': punctuated equilibrium.

For animals, the definition of different species is the lack of sexual reproduction between members of those species. For bacteria this definition cannot be used. Bacteria can sometimes share their genetic content, which is a way of sexual reproduction, and even members of different species can sometimes do this. This may actually be one reason why bacteria are so successful: the sharing of advantageous properties may enabled evolving species to become even more succesful. Their success depends on the selective pressures that are applied. This may sound very theoretical, but the truth is that the 'emergence' of antibiotic resistant bacteria is evolution as we speak. In our exhibit 'Antibiotics' it is explained that the use of antibiotics in medicine has resulted in resistance to antibiotics. Two mechanisms are responsible for the spread of antibiotic resistance among bacteria: every once in a while spontaneous mutations are formed that result in resistance (many bacteria are re-inventing the wheel!) but some bacteria simply 'steel' the DNA of their counterparts that have learned to deal with antibiotics. So, mutations and DNA sharing are the tools to generate diversity and increases the chance of a best fit. The selective pressure that leads to the spread of resistance is our use of antibiotics that selects for bacteria that are resistant. The battle between bacteria and man--the result of evolution.

Last Updated on Sunday, 01 March 2009 18:45