World Science News in Review
MIT Undergraduate Research Journal 19, 12 (Spring 2010)
Bacterial Behavior Sheds Light on Game Theory
Credit: Eshel Ben Jacob, ScienceDaily
Bacillus subtilis colonies.
The study of game theory, the science of how and why individuals make certain choices during competitive situations, has recently taken an interesting turn. Researchers have begun investigating the behavior of single-celled organisms in the hope of applying any newfound knowledge to human interactions.
Scientists at the University of California, San Diego’s Center for Theoretical Biological Physics have been using theoretical mathematics, chemistry, and physics to model the genomic and proteomic interactions among colonies of Bacillus subtilis under conditions of environmental stress.
Under stress, a bacterium faces two options. It can undergo sporulation, a process that involves more than 500 genes, in which the bacterium places a copy of its genome in a durable capsule known as a spore. These spores, which are extremely durable even during harsh conditions, can then germinate into new bacteria. The mother cell that sacrifices its genome to form the spore then bursts open releasing its intracellular contents to the environment.
The other option for the bacterium is to enter the “competence intermediate state” in which it makes its membrane more permeable to its extracellular environment so that it can assimilate the cellular contents released by other bacteria that have sporulated. Though this option may allow for survival, the bacterium risks death.
UCSD physics professor José Onuchic explains how these two options present a Prisoner Dilemma-like predicament: “It pays for the individual cell to take the risk and escape into competence only if it notices that the majority of the cells decide to sporulate. […] But if this is the case, it should not take this chance because most of the other cells might reach the same conclusion and escape from sporulation.”
The conclusion of the “game” is that only ten percent of the bacteria enter the “competence intermediate state.” The scientists have found that the decision a bacterium makes is dependent upon the chemical signals being released by its neighboring bacteria. Moreover, though the researchers keep refining their studies, they conclude that stochastic processes still pervade the decisions the bacteria make. Onuchic explains: “Another interesting fact is that the same cells in the same environment, in this case, bacteria in the colony, can actually in a statistical matter choose two different outcomes: sporulation or competence.”
The researchers hope their studies will have applications in sociology, economics, and even cancer biology.
http://murj.mit.edu/article.php?type=5&id=16
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