Morphological Effects on Bacterial Brownian Motion: Validation of a Chiral Two-Body Model

We systematically investigate how flagellar morphology governs the stability of bacterial Brownian motion, evaluating the effectiveness of a simplified chiral two-body model. This model, which effectively captures the specific bacterial morphology and significantly reduces computational cost, is used for simulating bacterial Brownian motion. Our results demonstrate that the model accurately reproduces the Brownian motion of bacteria for contour lengths $\mathrm{\Lambda }\ge 5.0$~\si{μm}, helix radii $0.2\le R\le 0.5$~\si{μm}, and pitch angles $\pi \mathrm{/}6\le \theta \le 2\pi \mathrm{/}9$. We find that the translational and rotational velocities of bacteria depend linearly on the motor rotation rate, independent of dynamic viscosity. Increasing helix radius and contour length leads to more elongated trajectories and enhances their linearity. Furthermore, longer contour lengths improve the stability of the bacterial forward motion. Collectively, these findings demonstrate the essential role of flagella in stabilizing bacterial Brownian motion and confirm the effectiveness of the chiral two-body model for simulating this phenomenon.