Fig. 1

Rotation of a fluorescent polystyrene bead attached to an archaellum of a cell immobilized to a glass surface. a Schematic of the experimental set-up. b Sequential micrographs of a rotating 490-nm-diameter bead captured in 10 ms intervals. Scale bar, 0.5 μm. c Schematic illustration of our optical path set-up between the equivalent sample plane (eSP) of the optical microscope and CCD camera to track three-dimensional (3D) motion of a bead as point light source. Half of the blue light is diffracted by a wedge prism, which is located at the equivalent back focal plane of the objective, and so two separate images are focused on the camera plate. d 3D plot of location of the bead bound to an archaellum over time. Different colors represent height from the glass surface. e xy-trajectory of bead position (dots) and representative one rotation (thin black line; starting from the open circle and ending at the closed circle). Upper, raw data. Lower, same dataset reoriented in 3D so that the circular rotation is coincident with the xy-plane of the plot. f Examples of time course of rotation in clockwise (CW; upper) and counter-clockwise (CCW; lower) directions. g Histograms of rotational rate for CW (upper) and CCW (lower). In d–g, 210-nm-diameter beads were used as markers