MULTIPLE FACTORS UNDERLYING THE MAXIMUM MOTILITY OF ESCHERICHIA-COLI AS CULTURES ENTER POSTEXPONENTIAL GROWTH

Motility and chemotaxis allow cells to move away from stressful microe nvironments. Motility of Escherichia coli in batch cultures, as measur ed by cell swimming speed, was low in early-exponential-phase cells, p eaked as the cells entered post-exponential phase, and declined into e arly stationary phase. Transcription from the flhB operon and synthesi s of flagellin protein similarly peaked in late exponential and early post-exponential phases, respectively. The increase in swimming speed between early-exponential and post-exponential phases was correlated w ith twofold increases in both flagellar length and flagellar density p er cell volume. This increased investment in flagella probably reflect s the increased adaptive value of motility in less favorable environme nts. The decrease in speed between post-exponential and stationary pha ses was correlated with a threefold decrease in torque produced by the flagellar motors and presumably reflects decreased proton motive forc e available to stationary-phase cells.