Figure 4 : Rotational measurements of the MotPS motor under high viscous conditions.

From: Load- and polysaccharide-dependent activation of the Na+-type MotPS stator in the Bacillus subtilis flagellar motor

Figure 4

(a) Torque of the MotPS motor measured using a 1.0-μm bead in media containing 0%, 2%, 4%, 6%, 8% and 10% Ficoll 400 (w/v). (b) Speed increment in a single MotPS motor with a 1.0-μm bead attached in the presence of 10% Ficoll. The expression of the MotPS stator was induced from an IPTG-inducible Pgrac promoter by addition of 0.1 mM IPTG, followed by incubation at 37 °C for 30 min and finally rotation measurements at 23 °C by tracking the position of 1.0-μm beads attached to the partially sheared sticky filament in motility buffer containing 1.0 mM IPTG, 200 mM NaCl and 10% Ficoll. (c) Torque-speed relationship of the MotPS motor in the presence of 10% Ficoll 400 (w/v) Rotation measurements were carried out at 23 °C by tracking the position of 1.5-μm (orange), 1.0-μm (red), 0.8-μm (purple), 0.6-μm (cyan) and 0.5-μm (light green) beads attached to the sticky filament. At least twenty individual beads were measured. Lines indicate the torque-speed curves of the MotAB (magenta) and MotPS motors (blue and grey) shown in Fig. 2. Blue and grey lines indicate the torque-speed curves of the MotPS motors, which were expressed from the PmotAB and Pgrac promoter, respectively. (d) Effect of Ficoll 400 on torque generation by the MotPS motor. Torque versus frictional drag coefficient are plotted and fitted by second-order polynomial function. Squares and circles indicate two sets of data of the MotPS motor labelled with 1.5-μm (orange), 1.0-μm (red), 0.8-μm (purple), 0.6-μm (cyan) or 0.5-μm (light green) bead in the presence and absence of 10% Ficoll 400. Triangles show a set of data of the MotPS motor labelled with a 1.0-μm bead in media containing 2%, 4%, 6% and 8% Ficoll 400 (w/v).