Figure 3.

Examples of rotation angular velocity PDFs for RP437 (top panels), RP5232 (middle panels), and XLWU100 (bottom panels). Each panel represents measurements from a single bacterium, and three panels for each cell type show typical cell-to-cell variations. We define Ω > 0 (Ω < 0) to be CW (CCW) cell-body rotation. The experimental data (black dots) are fitted with a sum of two Gaussians (P = P_t + P_r) for RP437 and XLWU100 and to a single Gaussian (P_r) for RP5232. (A)–(C) The dotted vertical lines, indicated by Ω_t and Ω_r, mark the boundary for the two (tumble, run) rotation states. These boundaries are determined according to the criterion P_i(Ω_i)/P(Ω_i) = 75%, where i = t or r. (D)–(F) The rotation speed of smooth-swimming mutant RP5232 can be fitted well by a single Gaussian. (G)–(I) The cell-body rotation of XLWU100 (ΔfliC) is expected to be similar to what is seen in the classical rotation assay because flagellar filaments of XLWU100 are sticky to glass. P(Ω) for this mutant is bimodal, similar to RP437; however, the two Gaussian peaks are well separated and are about equal in height. Note that for this mutant, CW motor rotation corresponds to Ω > 0 by our definition. Despite cell-to-cell variations, almost all cells (∼10²) examined for each strain have similar characteristics as displayed. To see this figure in color, go online.