Bacteria have diverse 'personalities' and 'moods', according to new research published in the journal eLife.

For the study, researchers compared bacteria with exactly the same DNA sequences that had also been grown under identical conditions. These bacteria were placed in the same chemical environment and exposed to stimuli, such as food or toxins.

Despite the fact that they were almost identical, they responded in very different ways.

"Each bacterium seems to have its own personality," said Johannes Keegstra from the AMOLF Institute in Amsterdam. "For example, we found that the chemical concentration to which bacteria respond varies considerably between bacteria."

The researchers also found that the way each bacterium responded changed randomly and continually over time, even in environments where there were no changes in stimuli.

"We were really surprised by how drastic their mood swings are," Keegstra said.

The researchers think that this 'moodiness' is caused by chance events within cells.

"We think that the bacterial individuality we found is not due to either nature (DNA) or nurture (features of the environment), but rather to random events like molecular collisions inside the bacterium's single cell, a classic example of what physicists call 'noise'," Tom Shimizu, also from AMOLF, said.

This randomness, or 'moodiness', may be advantageous for a bacteria population as a whole when food is scarce. In that case, it is less important to respond to sensory cues, such as odours, than it is to efficiently explore space to locate a rare resource. Temperamental bacteria would do better at exploring large featureless areas because their moodiness helps them avoid coming back to the same place.

"The considerable variation in how moody the bacteria are, could mean that some bacteria act as scouts that explore far away territories for occasional but large gains, while others remain nearby and efficiently exploit local resources," Keegstra said. "Such a division of labour could be useful for the population as a whole."