Genetic circuit allows both individual freedom, collective good

Genetic circuit allows both individual freedom, collective good.

– extracts from the article –

Spore formation is a drastic choice because it requires the cell to kill itself to encase a copy of its genetic code in a tough, impervious shell. Though the living cell dies, the spore acts as a kind of time capsule that allows the organism to re-emerge into the world of the living when conditions improve.

“This time-travel strategy of waiting and safeguarding a copy of the DNA in the spore ensures the survival of the colony,” Ben-Jacob said. “But there are other, less desperate options that B. subtilis can take to respond to stress. Some of these cells turn into highly mobile food seekers. Others turn cannibalistic, and about 10 percent enter a state called ‘competence’ in which they bide their time and bet on present conditions to improve.”

Scientists have long been curious about how bacteria decide which of these paths to pursue. Years of studies have determined that each individual constantly senses its environment and continuously sends out chemical signals to communicate with its neighbors about the choices it is making. Experimental studies have revealed dozens of regulatory genes, signaling proteins and other genetic tools that cells use to gather information and communicate with one another.

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 competence.”

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