Noise results from random fluctuations in a signal; every circuit -- whether genetic or electronic -- responds to noise in its own way. In the case of B. subtilis, noise is undesirable in the sporulation timer but is a necessity for the proper function of the competence switch, the researchers said.
"Our study explains how the two opposite noise requirements can be satisfied in the decision circuitry in B. subtilis," Onuchic said. "The circuits have a special capacity for noise management that allows each individual bacterium to determine its fate by 'playing dice with controlled odds.'"
Ben-Jacob said the timer has an internal clock that is controlled by cell stress. The noise-intolerant timer typically keeps the competence switch closed, but when the cell is exposed to stress over a long period of time, the timer activates a decision gate that opens brief "windows of opportunity" in which the competence switch can be flipped.
Thanks to its architecture, the gate oscillates during the window of opportunity, he said. At each oscillation, the switch opens for a short time and grants the cell a short window in which it can use noise as a "roll of the dice" to decide whether to escape into competence.
"The ingenuity is that at each oscillation the cell also sends 'chemical tweets' to inform the other cells about its stress and attempt to escape," said Ben-Jacob, the Maguy-Glass Professor in Physics of Complex Systems and professor of physics and astronomy at Tel Aviv University. "The tweets sent by others help regulate the circuits of their neighbors and guarantee that no more than a specific fraction of cells within the colony will enter into
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