Scientists detect unexpected activity in “dead” bacteria : ScienceAlert

Scientists have detected unexpected activity in dormant bacterial spores, showing for the first time that even when they are normally “dead”, the organisms are still aware of their environment.

Using a stored supply of charged particles for energy, instead of their usual fuel, the bacteria could actively respond to tiny changes in nutrient levels to determine when to start waking up.

The discovery challenges our understanding not only of how disease spreads, but also how life could survive extreme conditions here on Earth and beyond.

“This work changes the way we think about spores, which were considered inert objects,” says molecular biologist and lead researcher Gürol Süel of the University of California, San Diego.

“We show that cells in deep dormancy 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.”

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The implications also extend beyond disease management here on Earth – it’s often thought that one way we might encounter alien life is in similar dormant states.

“If scientists find life on Mars or Venus, it’s likely to be in a dormant state, and now we know that a life form that appears to be completely dormant may still be able to think about its next steps,” says Süel.

Bacteria are generally pretty tough, but one of their key survival tactics is to be able to enclose themselves in spores, where they can remain in a dehydrated, dormant state surrounded by a protective coating for hundreds of years – surviving extreme heat, pressure and even outer space.

This is not just a deep sleep. Essentially, the bacteria are physiologically dead, without metabolism.

But somehow they know when the conditions are right to wake up again.

Spores are how diseases such as anthrax, caused by Bacillus anthracis bacteria, can survive for long periods without water or nutrients in the mail – within moments of exposure to suitable conditions, they are able to hydrate and restart their metabolism, allowing them to become infectious again.

But how exactly do spores know when to wake up? Responding to every drop of moisture or whiff of nutrients could mean a lot of wasted energy if the good times don’t last long. However, waiting for a celebration can also mean missed opportunities.

To tease this out further, Süel and his team tested thousands of idlers Bacillus subtilis spores. The bacteria are considered non-harmful to humans and also happen to hold the record for longest survival in space.

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They measured whether the spores could pick up multiple short-lived pulses of nutrients sent into their environment – ​​signals that generally wouldn’t be strong enough to trigger a spore to spring back to life.

As predicted, one or two of these nutrient pulses alone were not enough to wake up the bacteria. But over time, a cumulative effect seemed to occur. somehow, the bacteria were somehow able to keep score and reactivate after a certain number of signals.

The team was also able to monitor changes in spore activity in response to these short-lived signals and showed that the bacteria used stored energy in the form of potassium ions (K+) with each input.

This is like a capacitor in a circuit, storing energy for later use.

Using a mathematical model to explain what was happening, the team showed that each signal triggered the release of potassium ions, and over time the potassium ions became strong enough to start reawakening the bacteria. They called this the ’embedding and firing’ model of activation.

Illustration showing how bacterial cells decide when to wake up. (Lombardino & Burton, Science2022)

This is known as a cumulative signal processing strategy and prevents the bacteria from waking up too soon if the conditions aren’t quite right.

“These findings reveal a decision-making mechanism that operates in normally quiescent cells,” the researchers write in their paper.

In a way, this is a fairly well-known evolutionary strategy.

“The way the spores process information is similar to the way the neurons in our brain work,” says Süel.

“In both bacteria and neurons, small and brief inputs add up over time to determine if a threshold is reached. Once the threshold is reached, the spores begin their return to life, while the neurons fire an action potential to communicate with other neurons.”

However, unlike neurons, which are incredibly energy-hungry cells, the spores could do this without any metabolic energy, just stored potassium.

In a companion “Perspectives” article, microbiologists Jonathan Lombardino and Briana Burton of the University of Wisconsin-Madison say further study in other organisms known to enter a similar spore-like state, such as fungi, could help to further clarify what this means for life. wider.

“For example, could the extreme longevity of so-called hyperdormant spores be traced to initial K+ concentrations? they write.

There is more work to be done, but the discovery challenges our understanding of dormant bacteria – and also redefines how we might evaluate signs of alien life in the future.

The research has been published in Science.

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