The undead can think? How dormant bacteria can still calculate their return to life

When conditions get a bit too extreme, some bacteria are able to shut down into a dormant state where their life processes stop.

These ‘undead’ cells, called spores, can withstand immense stresses while in this state, including extreme heat, pressure, even the harsh conditions of outer space, and can remain this way for thousands of years.

Then, when conditions become favourable again, spores that have remained dormant for years can wake up and spring back to life in a matter of minutes – like a zombie rising from the grave.

Now scientists know  these bacterial spores have the extraordinary ability to evaluate their surrounding environment while still remaining in this physiologically dead state, according to new research published in Science.

They found that spores gradually release stored electrochemical energy and that allows them to calculate when it’s the right time to resume normal biological activity – even when environmental signals are vague and don’t clearly indicate favourable conditions.

A microscopy time-lapse movie depicts the color-coded electrochemical potential value overlaid on top of the phase image of a single spore. As revealed by the phase image, the spore remains dormant while exhibiting the ability to count stimuli, as indicated by the multicolor-coded flashes of electrochemical potential changes. Credit: Süel Lab, Kaito Kikuchi

“This work changes the way we think about spores, which were considered to be inert objects,” says Gürol Süel, a professor in the Department of Molecular Biology at the University of California San Diego in the US.

“We show that cells in a deeply dormant state have the ability to process information.

“We discovered that spores can release their stored electrochemical potential energy to perform a computation about their environment without the need for metabolic activity.”

Many species of bacteria form spores – partially dehydrated cells surrounded by a resilient protective coating – one of the most infamous being Bacillus anthracis, the bacterium spores which cause Anthrax.

Read more: How do human eggs stay dormant and reproductively healthy for decades in the ovaries?

Using a mathematical model and experiments with dormant Bacillus subtilis spores, Süel and his colleagues were able to determine that the bacteria were able to sense and count short-lived environmental signals too weak to trigger a return to life on their own.

They do this by releasing some of their stored potassium in response to each small input until a critical threshold is reached, switching the spore into an active state.

“The way spores process information is similar to how neurons operate in our brain,” says 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.”

A composite movie showing the phase contrast of a single spore (top left) to visualize the dormant state. A movie (top right) shows the color-coded electrochemical potential of the same spore. The plot (bottom left) shows the corresponding time trace of the electrochemical potential values changing over time. Finally, a corresponding bar plot (bottom right) visualizes the jumps toward the threshold for returning to life. Credit: Süel Lab

This finding has implications in the search for evidence of life beyond Earth.

“This work suggests alternate ways to cope with the potential threat posed by pathogenic spores and has implications for what to expect from extraterrestrial life,” says Süel.

“If scientists find life on Mars or Venus, it is likely to be in a dormant state and we now know that a life form that appears to be completely inert may still be capable of thinking about its next steps.”

Please login to favourite this article.