Decision making circuitry in bacteria

Bacteria make decisions one of which is to swim towards food (or away from repellents ) using molecular signaling networks inside its “body” — a single cell.

There is no “brain” in bacteria in the sense we use the word “brain” for multicellular life — since bacteria are single celled life forms. However, inside in these single cell life forms are molecular signaling networks working at different time scales that drive decision making required for its survival, most of which have been conserved in multicellular life forms too.

• When bacteria (E. coli) is in an environment with abundant nutrients, it continues to divide and does not try to move. [1]
• When conditions becomes worse, they make a decision to grow several nanometer sized motors attached to propellers (flagella) which allow it to swim. It also generates a navigation system that tells it where to go in search of food avoiding repellents along the way.
• They can sense molecule gradients (e.g. food molecule) as small as one molecular per micron in a background of 1000 molecules per cell volume. Their small “body” length of one micron prevent this high level of sensitivity to food detection using antenna on the ends of the cell (spatial gradient sensing). The random fluctuations (Poisson) of the background signal (sqrt(1000) ~ 30) would mask the one molecule per micron gradient that they can detect. These organisms instead sample the gradient over time and integrate it, as opposed to spatially integrating the…