Bacteria can be tough little guys. Faced with no food, a dose of antibiotics, intense UV light, or any other perilous conditions, they can survive by entering a kind of dormant hibernation-like state, shutting off all major functions until the coast is clear.

Science has known about this state for some time, but a team of biologists has now discovered a new survival method that switches the bacteria into a zombie mode, in which they temporarily remain in a just-about-active dozy state.

The new insight into bacterial survival tactics help to explain how bacterial infections can suddenly flare up even after they were seemingly conquered by a treatment of antibiotics. It might also provide some clues about how we can conquer one of humanity's biggest threats – antibiotic resistance.

Reporting in the journal Nature Communications, a team of scientists from the University of Amsterdam studied how Bacillus subtilis cells, a non-pathogenic bacterium you can find in soil, survive in a state of deep starvation. They specifically chose a type of B. subtilis that was unable to produce endospores, a protective coat that bacteria don to protect themselves from stressful conditions.

Along with the well-understood dormant state, they noticed a new unknown state.

“We saw clear differences between the active state, the dormant state and this state,” project leader Professor Leendert Hamoen, of the UvA’s Swammerdam Institute for Life Sciences, said in a statement. “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.”

They called it the “oligotrophic growth state”, which means “nutrient-poor growth.” It explains how bacteria can continue to divide and remain metabolically active, but at a much slower rate than usual, a bit like a zombie stumbling along with a glazed-over look. Crucially, when conditions improve, the bacteria is able to snap back and can continue to grow new colonies as normal. This means the “zombie state” is a much more effective method to survive hardship, like a barrage of antibiotics.

“The big question now is: do bacteria other than Bacillus know this trick too? If so, this fundamentally changes our outlook on bacteria,” Hamoen concluded. “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.”