Flow-induced bending of flagella controls bacterial surface behavior

Area of Science:

• Microbiology
• Biophysics
• Fluid Dynamics

Background:

• Bacterial surface behaviors are often attributed to biological signaling.
• Mechanical forces and appendage reorientation may also play a crucial role.

Purpose of the Study:

• To investigate how shear force-induced flagellar reorientation controls surface behavior in *Pseudomonas aeruginosa*.
• To understand the role of flagellar rotation in bacterial surface interactions under flow.

Main Methods:

• Utilized microfluidics and flagellar labeling for high-resolution imaging.
• Employed mutants with paralyzed flagella to assess the impact of rotation.
• Analyzed single-cell behavior under host-relevant shear conditions.

Main Results:

• Flagellar rotation promotes surface departure in *Pseudomonas aeruginosa* under shear.
• Two distinct cell subpopulations emerged based on flagellar position (upstream vs. downstream).
• Upstream flagella were bent by shear, blocking rotation, while downstream flagella could rotate, facilitating surface departure.

Conclusions:

• The geometric relationship between flow and flagella dictates bacterial surface behavior and cell fate.
• Mechanical forces, specifically shear-induced flagellar reorientation, generate subpopulations and control bacterial surface dynamics.
• This mechanism provides a novel understanding of bacterial adaptation to flow environments.