"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," explained Onuchic. "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. Observations have shown that indeed only about 10 percent of the bacteria enter into competence. But how they make this decision and which cells take this chance have been a mystery."
The researchers discovered in their study that the bacteria's game theory decision making process is far more advanced than the well-known game theory problem known as the Prisoner's Dilemma.
Classic Prisoner's Dilemma, when applied to two prisoners, gives them the following offer: If only one prisoner pleads guilty, the one that cooperates gets two years in jail while the other one gets six years. If both of them admit guilt, then they will be imprisoned for four years. However, if none of them pleads guilty, they go free with no punishment. The temptation is not to admit anything, but the prisoners never know whether or not the other prisoner cooperated and pled guilty.
Because the number of participants in a bacterial colony can be up to 100 times the number of people on earth, the bacteria need to construct a more complex form of game theory. The rapidly changing environmental conditions they face means also bacteria have limited time to decide.
"Prisoner's Dilemma for bacteria is more complex," said Ben Jacob. "Each bacterium must decide whether to become a spore; that is, to cooperate, or escape into competence, or take advantage of the others, while it has a limited time to decide while a clock is ticking. We discovered that each cell has an internal timer whose pace changes according to the stress it experiencesthe pace goes up for higher stress decisions such as in humans. Our internal clock speeds up under danger
|Contact: Kim McDonald|
University of California - San Diego