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For The First Time, Bacteria Seen Entering Strange 'Zombie' Mode to Survive Starvation

DAVID NIELD
24 FEB 2019

When starved of nutrients, some bacteria can survive by going into a deep sleep or 'zombie' mode, scientists have discovered – and it could help us learn more about how to treat infections in the future.

 

To be clear, that's zombie, as in almost dead and with natural functions shut down, not zombie as in feasting on the flesh of the living.

This never-before-seen survival strategy has been named oligotrophic (or 'nutrient poor') growth. All the processes in the single-celled organisms slow right down to an extremely low level, until more favourable conditions come back.

The researchers behind the study used the non-pathogenic bacteria Bacillus subtilis, and in particular a variety that couldn't form a protective coating called endospores – that's the other survival trick bacteria often use, surrounding themselves in this 'shield' and basically shutting down when harsh conditions are encountered.

Inside the endospore, the bacteria are in what's known as a 'dormant state'.

But in this latest experiment, the researchers found that when the bacteria were starved of nutrients, they couldn't retreat to their dormant state. But they also weren't active, so something else must have been occurring.

"We show that these starved cells are not dormant but are growing and dividing," said the team in their paper, albeit it very slowly.

 

The distinction from the endospore or dormant state is crucial: the bacteria continued to divide when in the new oligotrophic growth state, albeit about a hundred times slower than usual, which doesn't happen with endospores.

"We saw clear differences between the active state, the dormant state and this state," says lead researcher Leendert Hamoen, from the University of Amsterdam in the Netherlands. "Normally, Bacillus is rod-shaped; but the starved bacteria shrank until they were almost spherical."

"All kinds of processes that are normally active in the bacterium were altered. But they did not stop completely, as happens when the bacterium retreats to a spore in a dormant state."

Forming endospores also takes up a lot of energy for the bacteria, so much so that they can't always recover or 'wake up' properly. It seems the bacteria can actually bounce back from this new zombie state more easily – potentially returning after a dose of antibiotics has apparently seen them off.

Scientists are currently in a race to find new solutions for fighting bugs that have become resistant to our best antibiotics, something this latest research could help with.

 

It remains to be seen exactly how and why bacteria use this special zombie state, but future studies should be able to give us some answers.

The next challenge is to see whether oligotrophic growth can happen in other types of bacteria too. These microorganisms may be only made up of a single cell, but they continue to surprise scientists with the sort of complex tricks they're capable of.

"The big question now is: do bacteria other than Bacillus know this trick too?" says Hamoen. "If so, this fundamentally changes our outlook on bacteria. Apparently, they do not always have to form spores to survive."

"If more bacteria are found to be able to switch to this state, it will throw a whole new light on, among other things, how bacteria can escape antibiotics."

The research has been published in Nature Communications.