Projects -Fluorescent flagella -Swimming without flagella -Gliding motility -Twitching motility -Swarming motility -Fluorescent chemotaxis proteins -Chemotactic signaling studied by FRET -Models of the chemotactic system -Motor force generation -Switching under load

A bead assay. Switching under load Karen Fahrner attached beads of different sizes to flagellar filament stubs and monitored their directions of rotation. Clockwise intervals were longer at low speeds, below 50 Hz, but other changes were not marked. We know from earlier work that the torque generated by the motor (when spinning CCW) changes by only a few percent between 50 Hz and stall. However, it is thought that a fixed number of protons goes through the motor each revolution (about 1200). So, can it be that the motor measures proton flux? Recently, Junhua Yuan and Karen Fahrner examined motor switching at low loads, by attaching 100-200 nm gold beads to flagellar hooks (of cells lacking flagellar filaments) and monitoring their direction of rotation in media containing different concentrations of the viscous agent Ficoll. Contrary to the case at high loads, motor switching rates increased appreciably with load. Both the CW to CCW and CCW to CW switching rates increased linearly with motor torque. Evidently, the switch senses stator–rotor interactions as well as the CheY-P concentration. Reference Fahrner, K.A., Ryu, W.S. and Berg, H.C. Novel behaviour of the bacterial flagellar switch. Nature 423, 938 (2003). Yuan, J., Fahrner, K. A. & Berg, H. C. Switching of the bacterial flagellar motor near zero load. J. Mol. Biol. 390, 394-400 (2009).

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