This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Learning is often thought to require a brain. But learning is a broad concept that does not necessarily depend on neurons.
If an organism uses information from past experiences to shape its future decisions, it is also learning. Research from my lab, published in the journal PRX Life, shows that even a single bacterium can learn from experience, store memories of the past and use those memories to prepare for the future. Bacteria live in environments that change constantly and on many different timescales.
In the human gut, for example, nutrient levels go up and down, temperatures shift, and antibiotic threats come and go. To survive, a bacterium has to respond quickly to what is happening right now while still preserving useful information about what it recently experienced. Adapting too quickly leaves the bacterium vulnerable to changing conditions, while forgetting too readily makes it unable to anticipate a recurring threat.
How does a bacterium manage this balancing act? This question interested me as a computational biophysicist who studies how living systems process information and adapt to changing environments. To investigate whether single-celled organisms such as bacteria can learn from past experience, my colleagues and I used what's called a microfluidic device to track the behavior of tens of thousands of individual E. coli cells as we switched their nutrient supply on and off at different rates.
We found that bacteria not only react to current nutrient levels in their environment, they also keep track of their nutrient history to cope with changing conditions. If the bacteria were simply reacting to their present environment, they would respond to a sudden pulse of food in exactly the same way, regardless of whether their previous environment was stable or rapidly fluctuating. Instead, when exposed to the same influx of nutrients, bacteria that had just experienced a feast-and-famine environment adapted much faster than bacteria coming from a stable environment.
Because the immediate conditions were identical for both bacteria, we reasoned that the difference in their behavior must originate from a stored internal record of their past rather than a simple reaction to their present. In other words, the bacteria's past experiences were shaping their present behavior—they were learning. But where were these cells storing this information?
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