Figure 1

Schematic representation of the core chemotaxis pathway. Reduction in chemoattractant or increase in chemorepellant is sensed by membrane-bound methyl-accepting chemotaxis receptors. This activates CheA and triggers transphosphorylation. The phosphoryl group is then transferred to either CheY or CheB. Phosphorylated CheY is able to diffuse and bind to the FliM component of the flagellar motor, resulting in a change in motor rotation from counter-clockwise to clockwise. This causes a switch from smooth swimming to tumbling and hence a change in swimming direction. Phosphorylated CheB competes with the constitutively active methyltransferase CheR, causing demethylation of the receptors, which reduces their ability to activate CheA. This resets the rate of direction changing to pre-stimulus levels, a process known as adaptation.