A study of bacterial flagellar bundling

Area of Science:

• Microbiology and Biophysics
• Computational Fluid Dynamics

Background:

• Bacteria like Escherichia coli (E. coli) and Salmonella typhimurium (S. typhimurium) utilize multiple flagella for locomotion.
• Flagella are left-handed helices rotated by basal motors, creating a corkscrew motion for swimming.

Purpose of the Study:

• To develop and utilize a computational model simulating bacterial flagellar motion and hydrodynamic interactions.
• To analyze the influence of flagellar rotation direction and hydrodynamic forces on bacterial swimming behavior.

Main Methods:

• Employed Stokes flow equations to model fluid dynamics.
• Represented flagellar elasticity using elastic springs and motors with base torques.
• Utilized regularized Stokeslets and rotlets to describe fluid velocities generated by forces and torques.

Main Results:

• Simulations showed that counterclockwise rotation of all flagella can lead to bundling due to hydrodynamic interactions.
• A change in rotation direction of at least one flagellar motor resulted in tumbling behavior, characterized by flagellar separation and altered orientation.
• Analysis provided insights into the fluid dynamics governing these bacterial motility patterns.

Conclusions:

• Hydrodynamic interactions between bacterial flagella are crucial for motility.
• The direction of flagellar rotation dictates whether bacteria swim or tumble, offering a mechanism for chemotaxis.
• The computational model effectively captures the complex interplay between flagellar dynamics and fluid mechanics.