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.