Harvard University Department of Physics

Motile behavior of bacteria: flagellated bacteria possess a remarkable motility system based on a reversible rotary motor linked by a flexible coupling (the proximal hook) to a thin helical propeller (the flagellar filament). The motor derives its energy from protons driven into the cell by chemical gradients or electrical fields. The direction of the motor rotation depends in part on signals generated by sensory systems, of which the best studied analyzes chemical stimuli. Howard Berg’s research group is trying to learn how the motor works, the nature of the signal that controls the motor’s direction of rotation, and how this signal is processed by the chemical sensory system. The group is also studying non-flagellated bacteria that glide over solid surfaces by as yet unknown mechanisms. These questions are being approached by a variety of molecular-genetic and physical techniques, including fluorescence and fluorescence resonance energy transfer. The goal is an understanding of motility and sensory transduction at the molecular levels.