E. coli bacterium tumbling in bulk and close to surfaces: a simulation study

Area of Science:

• Microbiology
• Biophysics
• Computational Biology

Background:

• Microbial motility is crucial for survival and proliferation.
• Escherichia coli (E. coli) uses rotating flagella for propulsion, with flagellar reversal causing tumbling and surface detachment.
• E. coli exhibits hydrodynamic attraction to surfaces, influencing its residence time.

Purpose of the Study:

• To develop a computational model of E. coli motility incorporating flagellar flexibility and polymorphic conformations.
• To investigate the effects of flagellar properties and surface proximity on bacterial tumbling behavior.
• To explain experimental observations of prolonged bacterial run times near surfaces.

Main Methods:

• Utilized an extended Kirchhoff-rod theory to model flagellar mechanics, including flexibility and conformational changes.
• Performed hydrodynamic simulations using the multi-particle collision dynamics (MPCD) method.
• Determined tumble angle distributions in bulk fluid and near bounding surfaces.

Main Results:

• The model accurately reproduced experimental tumble angle distributions in bulk fluid.
• Increased hook stiffness narrowed tumble angle distribution and reduced flagellar dispersion during tumbling.
• Near surfaces, tumble angles shifted towards smaller values, and flagellar dispersion decreased.
• Bacterial reorientation favored forward movement, potentially explaining longer run times.

Conclusions:

• Bacterial motility and surface interactions are intricately linked.
• Flagellar properties significantly modulate tumbling dynamics and surface detachment.
• The model provides insights into E. coli's surface-associated behavior and prolonged run times.