Yes, bacteria can form memories too!
Microbiologists Roland Mathis and Martin Ackermann from Eawag and ETH Zurich have, for the first time, experimentally demonstrated that colonies of bacteria can form a kind of collective memory. This collective memory increases the colony’s tolerance to environmental stress, improving their chance of survival.
It has been well documented in previous studies that individual bacteria are able to form short spanning memories, which don’t normally last longer than 30 minutes. These latest findings suggest that when a colony has the ability to form a longer kind of collective memory, capable of lasting for up two hours after exposure to an environmental stressor, such as an increased salt concentration.
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The microbiologists made their discovery by looking at Caulobacter crescentus, a bacterium commonly found in fresh and seawater. This type of bacteria are able to tolerate various concentrations of salt and adapt, allowing them to survive in seawater containing more salt than freshwater.
The scientist used a computational modelling system to help explain their findings, and the conclusions were based on a combination of two main factors:
First, increasing salt concentrations causes a delay in cell division. Under salt stress, cell division pauses, thus synchronizing the cell cycles of the bacteria in the exposed area.
Second, the survival rate of each bacterium when exposed to higher salt concentrations depends on the bacterial cell’s position in the cell cycle at the time of the increased exposure.
By reflecting on the first factor, all the bacteria within the area where the salt concentration was increased had synchronised their cell cycles. Hence, the sensitivity of the overall population over time was affected and colonies of bacteria that were previously exposed to increased levels of salt were more tolerant to future increases of salt concentrations, according to the researchers.
Not only were the bacteria more tolerant, they may also become more sensitive to the changes in salt concentration than populations of bacteria that had had no previous exposure.
As Martin Ackermann, one of the co-authors of the study, stated in a media release, “If we understand this collective effect, it may improve our ability to control bacterial populations.”
Ackermann went on to say, “If you want to understand the behaviour and fate of microbial populations, it’s sometimes necessary to analyse every single cell”
Their findings were online published in the Proceeding of the National Academy of Sciences of the United States of America on March 7, 2016.
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