Dynamics of a bacterial flagellum under reverse rotation

Area of Science:

• Microbiology
• Biophysics
• Theoretical Biology

Background:

• Bacterial flagella exhibit polymorphic states, transitioning between normal, semicoiled, and curly-I forms.
• Flagellar rotation reversal initiates tumbling in E. coli, involving complex conformational changes.
• Existing models use extended Kirchhoff free energy but lack complete ground state energy data.

Purpose of the Study:

• Investigate the impact of ground state energy variations on reversely rotated flagellar dynamics.
• Determine if tuning free energy landscapes can fully account for observed flagellar polymorphism.
• Model the sequence of polymorphic states in bacterial flagella.

Main Methods:

• Utilized an extended Kirchhoff free energy model to describe flagellar elasticity.
• Simulated dynamics of a reversely rotated flagellum under varying ground state energies.
• Developed a state diagram to comprehensively map distinct dynamical states.

Main Results:

• Identified several distinct dynamical states for the reversely rotated flagellum.
• Tuning the extended Kirchhoff free energy landscape alone is insufficient to generate the intermediate semicoiled state.
• The model proposes a method to achieve the observed polymorphic state sequence.

Conclusions:

• The ground state energies significantly influence flagellar dynamics and polymorphism.
• The extended Kirchhoff free energy model requires modification or additional factors to fully capture flagellar conformational changes.
• Findings are applicable to other peritrichous bacteria due to conserved flagellar elastic properties.