When faced with danger, it’s good to be a bacterium. These single-celled organisms have arguably the best way of protecting themselves against hostile conditions: “Playing dead” on the molecular level.

They do this by forming spores, which are thick-walled, round or oval structures that don’t eat, grow, or reproduce but can survive extreme temperatures and high levels of disinfectants. Scientists refer to spores as dormant, but by all metrics, they’re nonliving.

“If you could take them to the hospital and hook them up to some equipment to determine if they're living or dead, you would pronounce them dead because there's nothing to measure,” Gürol Suel, a molecular biophysicist at UC San Diego, told The Daily Beast. “They seem to be doing nothing that you would typically associate with living cells.”

Suel and his lab study how spores can go from flatlining to fully revived in a friendly environment. On Friday, they published a surprising discovery in Science: These dormant cells can “count” pulses of beneficial conditions and reactivate once a certain threshold is met. These findings shift our understanding of bacterial spores and can even inform how researchers classify and attempt to resurrect ancient life forms they may find on Mars or other planets.

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