| any bacteria swim by means of a rotary motor, powered by an electrochemical potential, which drives a rigid helical filament. In Escherichia coli, peritrichous flagella form a bundle of filaments which generates thrust. Periods of smooth swimming are interrupted by periods of erratic motion, following disruption of the bundle, which occurs when some motors change, or try to change, their direction of rotation. Regulation of motor reversal provides the basis for patterns of motility and for chemotaxis.;The flagellar filaments of minicells were visualized using Differential Interference Contrast (DIC) microscopy. The ability to visualize rotating filaments was instrumental in revealing the nature of the defect of a mutant, called sag, unable to swarm in semi-solid agar. We were able to show that the filaments of this mutant undergo helical to straight transformations when in contact with solid surfaces, causing a loss in their ability to generate thrust. We further determined that the mutation resides in flgL, the gene encoding HAP3, which is located at the junction between the hook and the filament. Therefore, the stability of a normal filament when subjected to bending or torsional stress depends on how it is attached at its base.;Previous studies on the physiology of tethered motors have focused on behavior under high torque, low speed conditions. This thesis extends this work by investigating motor behavior at higher speeds. To this end, a method for tethering minicells of E. coli was developed. Tethered minicells were found to rotate at speeds up to 170 Hz. The torque-speed relationship and switching statistics of minicell motors were studied, mainly at room temperature. Speed was found to decrease by... |
