Figure 3. Flagellar rotation is CW-biased in the S. Typhimurium ΔrecA mutant.

The flagellar switching profiles of S. Typhimurium LT2 wild-type (WT), dead wild-type (dead), ΔrecA, ΔcheB (tumbling), and ΔcheY (running) cells were evaluated. The resulting histograms show the distribution of the change in the mean cellular angular velocity around the optical axis (Θ). A zero-centered peak, as displayed by dead cells and the ΔcheB tumbling mutant, is indicative of CW-biased flagellar rotation, and a peak with positive values, as displayed by the ΔcheY running mutant, CCW-biased rotation. The presence of two peaks, one zero-centered and the other centered at positive values, indicates a mixed population displaying both CW and CCW rotational patterns and thus a non-biased flagellar rotational pattern. For each strain, the results were obtained from four independent experiments of ten cells each.