Figure 2.

Bacteria orientation angles (ϕ) and swim speed components under no-flow conditions. (a) The simulated PDF of ϕ is uniform under circular or random swimming assumptions. (b) Assuming a constant swim speed (v = 22.3 μm/s), the corresponding velocity components along the x or y axes of the surface (v_x or v_y) have a characteristic U-shaped distribution, with their PDF peaking at ±v. (c) In reality, the measured swim speed of the bacteria is normally distributed (μ = 22.3 μm/s; σ = 4.6 μm/s at the beginning of the experiment). (d) The corresponding PDFs for v_x and v_y are M-shaped and symmetric about the origin.