SOS response the call for variation?

The adaptive abilities of bacteria to survive antibiotic treatments have long been noted in the scientific community. More importantly the prevalence of this rapid acquirement of antibiotic resistance is such that it occurs not so much by chance, but by an adaptive mechanism, but how does this happen?

The SOS response is a transcriptional response to environmental stress causing changes in the regulation of numerous genes leading to mutations in the genome. These mutations are suspected to be the possible origin of the adaptive mutations involved in antibiotic resistance.

A recent paper by Cirz, Ryan T. et. al used DNA micro arrays to study the genetic effects of the SOS response in Pseudomonas aeruginosa in the presence of the antibiotic Ciprofloxacin and the possible effects of inhibition of LexA cleavage on antibiotic resistance. P.aeruginosa infections are well known for being hard to eradicate when using antibiotic therapy due to evolution of antibiotic resistance. The results of the paper indicate that the SOS response during antibiotic treatments allows the organism to gain mutations with the potential of obtaining resistance. Although the SOS response in P.aeruginosa is not exactly the same as in other bacteria such as Escherichia coli it has the still allows the organism time to adapt.

References

Cirz, R. T., O'Neill, B. M., Hammond, J. A., Head, S. R., Romesberg, F. E. (2006). Defining the Pseudomonas aeruginosa SOS Response and Its Role in the Global Response to the Antibiotic Ciprofloxacin. Journal of Bacteriology, 188, 7101-7110

Cirz, R. T., Chin, J. K., Andes, D. R., de Crecy-Lagard, V., Craig, W. A., Romesberg, F. E. (2005). Inhibition of Mutation and Combating the Evolution of Antibiotic Resistance. PLoS Biology, 3, 1024-1033

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Are Mutations The Solution???

Ever wondered how it is that organisms have been able to adapt to so many of the changes that our world has undergone since their creation? How is it the new species have evolved through all of the changing environments?

Of course Darwin proposed an answer to this question with his accredited ‘Natural Selection’ theory which says that animals that have a mutation that increases their fitness within that environment will be selected for, thus leading to the whole populations’ adaptation and possibly evolution into a new species.

While this theory makes sense, how is it that a mutation happens to be there at exactly the right time?

An article by Hersh, Ponder, Hastings and Rosenberg outlines an experiment conducted that showed that perhaps the randomness in timing of these mutations may not in fact be as arbitrary as Darwin surmised. It may be that the SOS response to mutations or stresses from the environment involves up regulating proteins that lead to more mutations (and hence adaptations) to possibly counteract the stress being put on the organism. The article brings to light the fact that organisms may not be innocent bystanders to environmental pressures; they may in fact be programmed to adapt and survive and hence mutations become the solution as well as the problem.

Student Number: 41164772
REFERENCES

PRIMARY: Hersch.M.N.,Ponder.R.G.,Hastings.P.J.,Rosenberg.S.M.(2004),Adaptive mutation and amplification in Escherichia coli: two pathways of genome adaptation under stress,Research in Microbiology,155(5),352-359

SECONDARY: Gene, M.(2005), Evolution under intrinsic control