Electric countdown timer tells sleeping spores when to wake up

Sometimes procrastination pays off. When their environment becomes too stressful, many bacteria stuff some of their innards into super-tough packets called spores, which die off and wait – potentially for centuries – for things to get better. How do these seemingly dead spots detect the optimal conditions for awakening? A new study in Science reveals that bacterial spores can decide when to wake up by setting an electric alarm.

Starvation, radiation, scorching heat, freezing cold, even the vacuum of space – nothing is of particular concern to a spore. But they seem “useless” otherwise, says study author and biophysicist Gürol Süel of the University of California, San Diego. “If you took these cells to the hospital,” he says, “they would be pronounced dead when they arrived.”

Spores are only indestructible when dormant. They must therefore avoid waking up (or “germinating”) when conditions are unfavorable, explains biochemist Peter Setlow of the University of Connecticut, who was not involved in the study: “If you make the wrong decision and you come back to life, you are dead.”

This study reveals one way the spores make this decision. To form a spore, a bacterium creates a copy of its DNA, packs it into a small compartment, wraps it all in a protective layer, and then bursts open, releasing the spore (and dying in the process). The forming spores store charged potassium ions, creating a “biological capacitor” that stores electrical energy, says Süel. Each time the spore encounters nutrients, some of its potassium store escapes, dissipating some of the charge. Once this happens enough times, the stored energy drops below a threshold and the spore germinates – with a reasonable chance of not starving.

“This is a significant advancement in the field,” Setlow says. “It brings a whole new way of thinking about germination.” Knowing how spores “count” nutrients could improve food safety, as spore-forming bacteria can survive harsh sterilization procedures and relive to cause food poisoning. Dormancy also helps certain pathogens escape attack; waking them up early could improve treatments, so “there’s a lot of applied interest in how to get the spores to germinate quickly,” Setlow adds.

The study results suggest that ionic countdowns may be fundamental to life on Earth, Süel says. Neurons also rely on electricity to know when to fire; the researchers found that the formulas that describe neurons also predict the behavior of spores. Venus’ fly traps close with an electrical countdown, and all cells harness ion flows to process energy.

“These electrical potentials are not a recent invention. They are billions of years old,” says Süel. “What other aspects of biology can we better understand by keeping in mind that it’s not just about the expression of genes, proteins and DNA, but about these charged ions?”

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