Phage hunt blog: The Evolution of Bacteriophages

The theory of evolution is one that can be difficult to prove – the natural evolution of a species happens over thousands of years because of long reproduction times. This is what makes bacteria and bacteriophages such prime specimens to test on: short reproductive times of around twenty minutes means that scientists can breed a significant number of generations within a short amount of time. Phages also have high mutation rates and large population sizes.

Another advantage of phages is that the can be frozen in stasis – this means that a sample can be frozen without the phage being harmed, so once the sample of phages is warmed they are just as alive as they were when they were frozen. This is useful because a sample can be frozen for an indefinite length of time, and the bacteriophages can then be experimented on at a later date after the initial experiment. This is important because of the high rate of mutation – if the phages are left able to reproduce then when the scientists wish to use them to test on, the genome (genetic material) of the phages will be different to the original phages. This means the experiment could yield different results.

There are a number of ways mutations can affect the phage:

  • the phage can adapt to infect different hosts (eg. different species of bacteria or other organism)
  • the phage can adapt to be able to survive in different conditions (eg. high acidity or low salt concentrations in the environment)
  • the phage can adapt to either high or low temperatures
  • the phage can adapt to counteract a deleterious mutation (a deleterious mutation is one that leaves the phage less fit)
  • the phage can adapt to affect the host bacteria in a negative way (acts less like a parasite and more like a disease)

There are other ways that bacteriophages can adapt or change within their environment. Phages are sometimes able to exchange genes in a way similar to sex. In the case of two different phages coinfecting the same bacterial cell, the phages can swap parts of their genome, effectively changing their genetic code. This is useful to overcome a condition called Muller’s ratchet, which is when a phage has accumulated many detrimental deleterious mutations. Due to phages mostly asexual nature, these mutations are very hard to get rid of and therefore can lead to the extinction of that phage species.

Phages can also go through coevolution with another species; this species is most likely to be the phages main host that it infects. The host bacterial cell evolves to try prevent infection from phages, and the phages then evolve to increase its ability to infect the bacterial cell. In a laboratory environment, this mimics the predator/prey situation of prehistoric times and today, just on a micro scale.

I found this information on wikipedia (it’s very difficult finding information that isn’t a peer reviewed paper that is hard to read) however if you do want to read the more scientific experiments then there are some references in the wikipedia article at http://en.wikipedia.org/wiki/Bacteriophage_experimental_evolution

Still hunting (somehow I took everyone’s luck)

Jess

 

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One Response to Phage hunt blog: The Evolution of Bacteriophages

  1. emphnz says:

    I found a cool idea where the phages are not looked at as a whole, but as modules working together. its interesting to think of a very different form of evolution from how we usually understand it. and whether or not this proves to be a viable hypotheses, it shows how little we really know about phages and evolution.
    https://www.princeton.edu/genomics/botstein/publications/1980_Botstein_Theory.pdf

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