Behind their deceptive, single-celled simplicity, bacteria have managed to evolve a number of complex survival strategies. It is known that some bacteria can enter a dormant state, essentially "sleeping" to avoid periods of starvation or attack from extreme conditions. A newly discovered metabolic state, in between dormancy and activity, has now been discovered by an international team of scientists. This previously unknown zombie-like state involves the organism slowing down all its metabolic processes in order to survive for extended periods of time when its environment is starved of nutrients.

From entering a state of hibernation to hoarding large volumes of antibiotics allowing its neighbors to grow unharmed, bacteria have evolved incredible survival tactics. Now a new strategy has been discovered, led by a team of biologists from the University of Amsterdam's Swammerdam Institute for Life Sciences.

The study began by looking at Bacillus subtilis, a common and harmless bacterium that is known to enter long dormant states by reducing into a form called an endospore. There are some mutant forms of this bacteria that are unable to form endospores yet still can survive long periods of starvation. Examining this survival strategy revealed a new way bacteria can survive extreme stress.

"We saw clear differences between the active state, the dormant state and this state," explains Leendert Hamoen, a researcher working on the new study. "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. The bacteria even continued to divide. Only not once every forty minutes, but once every four days; more than a hundred times slower than usual."

This new process has been dubbed oligotrophic growth, meaning nutrient-poor growth, by the researchers, and is defined as a slow metabolic phase occurring in nutrient-poor environments. Interestingly the study showed the bacteria, once in its oligotrophic phase, was much more tolerant to some antibiotics and oxidative stresses. This suggests it could be one strategy bacteria uses to avoid destruction from antibiotics.

"The big question now is: do bacteria other than Bacillus know this trick too? If so, this fundamentally changes our outlook on bacteria," says Hamoen. "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 new study was published in the journal Nature Communications.