Wednesday, November 17, 2010

bacterial communities trump game theory


Video - Game Theory explained.

ScienceDaily | When it comes to gambling, many people rely on game theory, a branch of applied mathematics that attempts to measure the choices of others to inform their own decisions. It's used in economics, politics, medicine -- and, of course, Las Vegas. But recent findings from a Tel Aviv University researcher suggest that we may put ourselves on the winning side if we look to bacteria instead.

According to Prof. Eshel Ben-Jacob of Tel Aviv University's School of Physics and Astronomy, current game theory can't account for bacteria's natural decision-making abilities -- it's just too simplistic. Understanding bacteria's reactions to stressful and hazardous conditions may improve decision-making processes in any human arena from everyday life to political elections.

In a recent article published in the Proceedings of the National Academy of Science (PNAS), Prof. Ben-Jacob and his fellow researchers outline how decisions made by communities of bacteria trump game theory. "When human beings make a decision," he says, "they think they're being rational. We now understand that they're influenced by superfluous 'noise,' such as their cognitive state and the influence of others." Bacteria, he explains, are both simpler and more sophisticated -- they can more effectively control this superfluous noise and make group decisions that contribute to the well-being of the entire bacterial colony.

Looking out for the whole
Bacteria live in complex colonies that can be 100 times as numerous as the population of Earth. Under stressful circumstances, bacteria have demonstrated a capacity to assess the noisy and stressful environment around them, filter out what's relevant and what's not, and make decisions that ensure the survival of the colony as a whole.

For example, one bacterial response to starvation or poisoning is that a fraction of the cells "sporulate," enclosing their DNA in a capsule or spore as the mother cell dies. This, says Prof. Ben-Jacob, ensures the survival of the colony -- when the threat is removed, the spores can germinate and the colony grows again.

During this process, the bacteria "choose" whether or not to enter a state called "competence," in which bacteria change their membranes to more easily absorb substances from their neighboring, dying cells. As a result, they recover more quickly when the stress is gone. According to Prof. Ben-Jacob, it's a difficult choice -- in fact, a gamble. The decision to go into a state of competence only pays off if most of the cells decide to sporulate.

Indeed, observations show that only about 10% of cells decide to go into competence. So why don't all bacteria attempt to save themselves? Bacteria don't hide their intentions from their peers in the colony, he explains -- they don't lie or prevaricate, but communicate their intentions by sending chemical messages among themselves. Individual bacteria weigh their decisions carefully, taking into account the stress they are facing, the situation of their peers, the statistics of how many cells are sporulating and how many are choosing competence.