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Force-extension measurements on bacterial flagella: triggering polymorphic transformations.

Nicholas C Darnton1, Howard C Berg

  • 1Rowland Institute at Harvard, Harvard University, Cambridge, Massachusetts 02142, USA.

Biophysical Journal
|December 19, 2006
PubMed
Summary
This summary is machine-generated.

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Bacterial flagella proteins (flagellin) can change helical shapes. Researchers demonstrated controlled, reversible transformations between these bacterial flagella forms using optical tweezers, revealing insights into bacterial motility.

Area of Science:

  • Microbiology
  • Biophysics
  • Structural Biology

Background:

  • Bacterial flagella exhibit diverse helical shapes influenced by environmental factors.
  • A geometric model predicts 12 discrete helical states (polymorphic forms) arising from flagellin protein structure transitions.
  • Understanding flagellar polymorphism is crucial for comprehending bacterial motility and adaptation.

Purpose of the Study:

  • To experimentally demonstrate and characterize the controlled, reversible transformations between bacterial flagella polymorphic forms.
  • To investigate the mechanical properties and force-dependent transitions of flagellin polymers.

Main Methods:

  • Utilized purified long polymers of flagellin.
  • Employed optical tweezers to apply force and measure force-extension curves of single flagellar filaments.

Related Experiment Videos

  • Recorded progressive filament transformations during stretching.

    • Main Results:

    • Demonstrated controlled, reversible transformations between different polymorphic forms of flagellin polymers.
    • Measured elastic stretching with a bending stiffness of 3.5 pN x µm² for both normal and coiled forms.
    • Observed force-threshold-induced transformations to longer polymorphic forms (4-7 pN for normal, 3-5 pN for coiled).
    • Transformation force and extent were non-deterministic and dependent on stretching rate, indicating activation energy.

    Conclusions:

    • The study provides experimental evidence for the predicted flagellar polymorphic transitions.
    • Flagellar shape changes are mechanically driven, involving cooperative protein structural rearrangements.
    • Polymorphic transitions are stochastic processes influenced by applied force and kinetics, with implications for bacterial behavior.