Bacteria exploit a polymorphic instability of the flagellar filament to escape from traps

Area of Science:

• Microbiology
• Biophysics
• Cellular Motility

Background:

• Many bacteria use polar flagella for locomotion, enabling movement in diverse environments.
• Navigation involves forward/backward swimming and direction changes, crucial for survival in soils, sediments, and mucus.

Purpose of the Study:

• To investigate an alternative motility strategy employed by bacteria when encountering obstacles.
• To characterize a newly discovered flagellar behavior in *Shewanella putrefaciens*.

Main Methods:

• High-speed microscopy was used to observe the swimming dynamics of *Shewanella putrefaciens* with fluorescently labeled flagella.
• Microscopy data was combined with biophysical modeling to understand the mechanics of the flagellar change.

Main Results:

• When stuck, the polar flagellum undergoes a polymorphic change, forming a spiral around the cell body.
• This spiral configuration enables escape through a screw-like backward motion, triggered by flagellar rotation reversal and torque.
• The bacteria can revert to normal swimming after escaping, indicating a reversible mechanism.

Conclusions:

• A novel, reversible bacterial motility mode involving flagellar shape transformation was discovered.
• This screw-type propagation is likely a widespread mechanism for bacteria to escape traps in complex, structured environments.
• The findings expand our understanding of bacterial navigation and adaptation strategies.