Bacteria can count even in deep sleep

Dormant bacteria spring back to life in favourable conditions after evaluating their surroundings.

A microscopy image reveals several spores with their electrochemical potential colour-coded according to the strength of the signal. | Photo Credit: Süel Lab (Kaito Kikuchi and Leticia Galera)

“How do dormant spores decide to wake up? Turns out that they can count in their sleep using electricity!” tweeted biologist Kaito Kikuchi of University of California San Diego (UCSD) on October 6 after his paper on this age-old question was published in Science.

When faced with starvation and stress conditions, bacteria are known to enter a deep dormant state in which life processes stop. This dormancy allows these cells, called spores (partially dehydrated cells surrounded by a resilient protective coat), to withstand extremes of heat, pressure, and even the harsh conditions of outer space. Many bacterial species can remain dormant for thousands of years. Eventually such spores spring back to life in minutes in favourable conditions by re-hydrating and restarting their metabolism and physiology.

Kikuchi and his associates at UCSD have discovered that spores have an extraordinary ability to evaluate their surrounding environment while remaining in a physiologically dead state. They found that spores use stored electrochemical energy like a capacitor to determine whether conditions are suitable for a return to normal life.

Kikuchi and his colleagues tested whether dormant Bacillus subtilis spores could sense short-lived environmental signals that were not strong enough to trigger a return to life. They found that spores were able to count such small inputs and even decide when to exit the dormant state.

“The way spores process information is similar to how neurons operate in our brain,” said Süel. “In both bacteria and neurons, small and short inputs are added up over time to determine if a threshold is reached. Upon reaching the threshold spores initiate their return to life, while neurons fire an action potential to communicate with other neurons.”

This new information about spores, the researchers believe, reframes popular ideas about cells that seem dead. Such findings hold implications for evaluating life on objects such as meteors as well as space missions seeking evidence of life.