How dormant bacteria spores sense when it’s time to come back to life

Bacteria go to extremes to handle hard times: They hunker down, building a fortress-like shell around their DNA and turning off all signs of life. And yet, when times improve, these dormant spores can rise from the seeming dead.

But “you gotta be careful when you decide to come back to life,” says Peter Setlow, a biochemist at UConn Health in Farmington. “Because if you get it wrong, you die.” How is a spore to tell?

For spores of the bacterium Bacillus subtilis, the solution is simple: It counts.

These “living rocks” sense it’s time to revive, or germinate, by essentially counting how often they encounter nutrients, researchers report in a new study in the Oct. 7 Science.

“They appear to have literally no measurable biological activity,” says Gürol Süel, a microbiologist at the University of California, San Diego. But Süel and his colleagues knew that spores’ cores contain positively charged potassium atoms, and because these atoms can move around without the cell using energy, the team suspected that potassium could be involved in shocking the cells awake.

So the team exposed B. subtilis spores to nutrients and used colorful dyes to track the movement of potassium out of the core. With each exposure, more potassium left the core, shifting its electrical charge to be more negative. Once the spores’ cores were negatively charged enough, germination was triggered, like a champagne bottle finally popping its cork. The number of exposures it took to trigger germination varied by spore, just like some corks require more or less twisting to pop. Spores whose potassium movement was hamstrung showed limited change in electric charge and were less likely to “pop” back to life no matter how many nutrients they were exposed to, the team’s experiments showed.

Changes in the electrical charge of a cell are important across the tree of life, from determining when brain cells zip off messages to each other, to the snapping of a Venus flytrap (SN: 10/14/20). Finding that spores also use electrical charges to set their wake-up calls excites Süel. “You want to find principles in biology,” he says, “processes that cross systems, that cross fields and boundaries.”

Spores are not only interesting for their unique and extreme biology, but also for practical applications. Some “can cause some rather nasty things” from food poisoning to anthrax, says Setlow, who was not involved in the study. Since spores are resistant to most antibiotics, understanding germination could lead to a way to bring them back to life in order to kill them for good.

Still, there are many unanswered questions about the “black box” of how spores start germination, like whether it’s possible for the spores to “reset” their potassium count. “We really are in the beginnings of trying to fill in that black box,” says Kaito Kikuchi, a biologist now at Reveal Biosciences in San Diego who conducted the work while at University of California, San Diego. But discovering how spores manage to track their environment while more dead than alive is an exciting start.