Bacteria Store and Pass on ‘Memories’ for Future Generations, Use Iron-Based Recollection To Improve Swarming Efficiency

As single-celled organisms, bacteria do not possess a brain, mouth, or other senses like ours. While it is easy to think that memories cannot be created in such situations, it has been discovered that bacteria create memories and transmit them to the next generations.

Bacterial Memory System

Escherichia coli (E. coli) is one of the most well-studied organisms on Earth, but scientists are still discovering how they survive and spread. Researchers at the University of Texas and the University of Delaware have uncovered a potential memory system that allows these microorganisms to remember past experiences for several hours and even generations. The study reported their findings, "A heritable iron memory enables decision-making in Escherichia coli."

The memory discovered by scientists is not the same as the conscious human memory. To their knowledge, this kind of bacterial memory has not been unveiled. The bacterial memory described by the team also provides insight into how information experience can influence current decision-making.

Bacteria do not possess brains but can collect information from their environment. If they have frequently encountered that environment, they can store data and quickly access it later for their benefit.

Led by molecular bioscientist Souvik Bhattacharyya from UT, the research team conducted more than 10,000 bacterial swarm assays. It aims to test if E. coli bacteria on a single plate would swarm together into one migrating mass that moves with the same motor. This behavior generally indicates cells joining up to find a suitable environment efficiently. Meanwhile, E. coli cells clumping into a sticky biofilm shows colonization of a nutritious surface.

In initial experiments, the E. coli samples were exposed to various environmental factors to find the conditions that trigger swarming the fastest. It was found that intracellular iron was the strongest predictor of bacterial motion. Low iron levels are connected to faster and more efficient swarming, while higher levels are associated with a more settled lifestyle.

Among the first-generation E. coli cells, this behavior seemed to be an intuitive response. After experiencing just one swarming event, however, the cells that experienced low iron levels later in life were faster and more efficient at swarming than before.

Moreover, the 'iron memory' was also found to be passed on to at least four successive generations of daughter cells, the product of mother cells that split into two new cells. By the seventh generation of daughter cells, that memory was lost, although it could be regained if artificially reinforced by the scientists.

Role of Iron in Bacterial Survival

Before oxygen became present in the Earth's atmosphere, iron was utilized by early forms of life for their cellular processes. This element is critical in the origin of life on our planet and in the evolution of life.

Iron is linked to multiple stress responses in bacteria. Forming an intergenerational memory system around it makes a lot of evolutionary sense. A memory system based on iron could help E. coli adapt to antibiotics or poor environmental conditions.