"Only a portion of the bacteria in a colony will form spores and only portion of the bacteria produce subtilisin, and we were interested in probing the genetic basis for this," Igoshin said. "How is it decided which cells become spores and which don't?"
Igoshin, a computational biologist, used computer simulations to help decipher and interpret the team's experimental results. He said the team found that fewer than 30 percent of individuals in a colony produce large quantities of the food-converting proteins. Even though the proteins benefit all members of the colony and help some cells to become spores, the cells that produce the proteins in bulk do not form spores themselves.
"There's a feedback loop, so that cells that start producing the proteins early get a reinforced signal to keep making them," Igoshin said. "We found that it's probabilistic events -- chance, if you will -- that dictates who is early and who is late. The early ones start working for the benefit of everyone while the later ones save valuable resources to ensure successful completion of sporulation program. Many cells will end up committing to sporulation before they had a chance to contribute to protease production"
Igoshin said a key piece of evidence confirming modeling predictions came in experiments that tracked genetically identical sister cells, some of which became protein producers and some of which didn't.
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