Oscillations In Continuous Culture Populations Of Streptococcus Pneumoniae: Population Dynamics And The Evolution Of Clonal Suicide

Main Category: Infectious Diseases / Bacteria / Viruses
Also Included In: Biology / Biochemistry
Article Date: 03 Dec 2008 - 6:00 PDT

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Agents that that kill the organisms that produce them or other, genetically identical members of their populations are intriguing puzzles for ecologists and other evolutionary biologists. How can such 'self-killing' agents, which, on first consideration, appear to engender a considerable disadvantage to the individuals that produce them, evolve and be maintained by natural selection?

Nevertheless, a number of seemingly suicidal processes have been observed in bacteria. In this study, we report on a similar mechanism in the commonly pathogenic bacteria, Streptococcus pneumoniae (pneumococcus).

When clinical as well as laboratory strains of pneumococcus are maintained in continuous culture (chemostats), their population densities oscillate by as much as a 100,000 fold. Using a combination of mathematical models and experiments we provide evidence that the population-wide die offs responsible for these oscillations are driven by the release of a toxin that either kills these bacteria directly or induces them to commit suicide, a 'suicidal' agent that may offer potential for the development of new antibiotics.

We postulate that the production of these suicidal 'agents' by individual streptoccocci prevent the invasion of other Streptococcus of the same or closely related species and hence, have evolved and are maintained by the 'protective' advantage they offer their populations.

Alas, even bacteria seem to adhere to the adage that you can win if you harm others to a greater extent than you harm yourself.

Proceedings of the Royal Society B: Biological Sciences

Proceedings B is the Royal Society's flagship biological research journal, dedicated to the rapid publication and broad dissemination of high-quality research papers, reviews and comment and reply papers. The scope of journal is diverse and is especially strong in organismal biology.

Proceedings of the Royal Society B: Biological Sciences