Abstract
The response regulator CheY is an intracellular signaling molecule that plays a central role in chemotaxis signaling in E. coli cells. Here, we show that changes in CheY-P concentration and flagellar motor rotation are highly correlated within a single cell after stimulation by the attractant l-serine. To monitor the CheY-P concentration and cellular behavior, FRET between CheY-YFP and CheZ-CFP and flagellar rotation were monitored simultaneously. The time required for recovery of the CheY-P concentration (FRET recovery time) and the duration of highly counterclockwise-biased flagellar rotation (CCW duration) were similar and depended on the strength of the stimulus. Both the FRET recovery time and the CCW duration varied from cell to cell, even at the same serine concentration. In cells adapted to serine, the sensitivity of the motor to CheY-P concentration shifted toward lower CheY-P levels relative to prestimulation cells. Thus, we could correlate the changes in CheY-P concentration with motor behavior during attractant adaptation.