Identical ΔfliM bacteria exhibit individuation of motion preferences. (A) 2D histogram of |v_pLead(t)| versus |v_pTrail(t)|, from datasets of two different ΔfliM mutant bacteria. The dashed line (slope = 1.0) is a guide to the eye to indicate translational motion (|v_pLead(t)| = |v_pTrail(t)|); the dashed circle is a guide to the eye to indicate rotational motion (|v_pLead(t)| ≠ |v_pTrail(t)|); the dotted green lines indicate the velocity threshold (|v_pLead,pTrail| = 0.3 μm/s) separating release actions and pull actions. Genetically identical bacteria exhibit distinct individual motion preferences: (i) rotation; (ii) translation. (B) Portion of trajectories from (top) bacterium (i), with schematic illustrating rotational motion, and (bottom) bacterium (ii), with schematic illustrating translational motion. In (B) the blue and red circles indicate positions of p_Lead and p_Trail, respectively.

Analysis of the velocity of leading pole p_Lead reveals distinct pulls and releases. (A) Schematic definition of an action in the velocity profile: For the ith action A_i, |v_pLead(A_i)| is the velocity amplitude, τ(A_i) is the duration time, and D(A_i) is the total displacement. (B) 2D histogram of the velocity amplitude of connected actions (A_i and A_i+1) for leading pole p_Lead. (C) Velocity amplitude |v_pLead(A)| as a function of duration τ(A) for the leading pole p_Lead in the trajectory of a single ΔfliM bacterium (N = 12,000 points); the color scale indicates the total displacement D(A). The two dashed lines (slope = -1.0) are guides to the eye indicating total displacements between 0.01 μm and 0.1 μm. (D) Histogram of the duration τ(A). The dashed line indicates the time threshold (τ_c = 0.2 s) separating release actions (red bars) from pull actions (blue bars). (E) Histogram of the velocity amplitude |v_pLead(A)|. The dashed line indicates the velocity threshold (|v_pLead,c| = 0.3 μm/s) separating release actions (red bars) from pull actions (blue bars). (F) Histogram of the displacement D(A) of release actions (red bars) and of pull actions (blue bars). In D–F the line is the Gaussian fit to the distribution.

Identical ΔfliM bacteria exhibit distinct orientation preferences. (Inset A) Schematic plot of the p_Lead action velocity vector; θ is the deviation angle between the p_Lead velocity vector and the body axis of the bacterium, with clockwise (counterclockwise) motion defined as positive (negative). (A) Normalized distribution of the deviation angle (θ), p(θ) calculated from 10 trajectories of different single ΔfliM bacteria, including approximately 180,000 images. (B) Distribution of deviation angle for a single bacterium, showing that single cells also exhibit orientational preference. In A and B distributions for release actions (red line) and pull actions (blue line) are decomposed from the entire trajectory.