Figure 3.

Measured speed versus radius of trajectory in comparison with numeric predictions by applying a simple hydrodynamic model. (a) Shown is the speed of bacteria with respect to the radius of curvature of trajectories for the four strains tested. The red line is the prediction by applying resistive force theory (with parameters specified in Table S1). The lower end of the line is set by the 5-nm minimal gap chosen between the cell body and the bottom surface in the model. Each data point represents measurements for an individual bacterium. (b) Shown are schematics showing the curvilinear trajectory of a bacterium when it swims close to a solid boundary. The cell body and its flagellar bundle rotate in opposite directions. The larger drag on the cell body at the location facing the surface exerts a lateral force in the opposite direction to that on the flagella (forces indicated in the figure) is shown. The net torque leads to a circular trajectory. To see this figure in color, go online.