Dynamic instability in the hook-flagellum system that triggers bacterial flicks

Area of Science:

• Microbiology
• Biophysics
• Biomechanical Engineering

Background:

• Bacterial motility, crucial for survival and infection, relies on flagellar propulsion.
• The run-reverse-flick (RRF) motility pattern involves complex flagellar and hook dynamics.
• Previous hypotheses for flick initiation centered on static Euler buckling of the hook.

Purpose of the Study:

• To elucidate the precise mechanism underlying flick initiation in monotrichous bacteria.
• To investigate the role of the flagellar hook's flexibility in bacterial motility.
• To determine if flick initiation involves static buckling or dynamic instability.

Main Methods:

• Analysis of forces and torques on the flagellar hook.
• Development of a mechanistic model for flick initiation.
• Calculation of the torque-stiffness ratio triggering dynamic instability.

Main Results:

• Flick initiation occurs via a dynamic instability, not static Euler buckling.
• This instability requires flexibility in both the flagellar hook and the flagellum.
• Observed flick initiation occurs at stresses below the static Euler buckling criterion.
• The model accurately predicts the onset of dynamic instability based on experimental data.

Conclusions:

• Bacterial flicks are driven by a dynamic instability mechanism.
• Hook and flagellar flexibility are essential for this motility behavior.
• The findings challenge previous static buckling hypotheses and offer a new understanding of bacterial flagellar dynamics.