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Modelling bacterial twitching in fluid flows: a CFD-DEM approach.

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This study models bacterial twitching motility in shear flows using computational fluid dynamics and discrete element methods. It reveals an optimal shear stress for upstream movement and predicts accumulation in groove surfaces.

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Area of Science:

  • Microbiology
  • Biophysics
  • Computational Science

Background:

  • Bacterial habitats frequently involve fluid flow, where twitching motility is crucial for colonization and biofilm formation.
  • Existing research on bacterial twitching is predominantly experimental, lacking models for shear flow conditions.
  • A fundamental understanding of how bacterial properties and environmental factors influence twitching in flow is needed.

Purpose of the Study:

  • To develop and validate a 3D Computational Fluid Dynamics (CFD) coupled with Discrete Element Method (DEM) model for bacterial twitching in shear flows.
  • To investigate the effects of fluid flow rate and surface topography on bacterial twitching motility.
  • To explore how factors like pili number, distribution, and environmental conditions impact bacterial movement.

Main Methods:

  • A 3D CFD-DEM model was developed to simulate rod-shaped bacteria, represented by spherical particles with dynamic Type IV pili springs.
  • The model was validated against the observed orbiting of immotile bacteria in shear flows.
  • Simulations were conducted on flat and groove surfaces under varying shear flow conditions.

Main Results:

  • The model successfully predicted upstream twitching motility of rod-shaped bacteria in shear flows.
  • An optimal range of wall shear stress was identified for efficient upstream bacterial twitching.
  • Bacteria were predicted to accumulate downstream of groove walls when twitching on grooved surfaces.

Conclusions:

  • The developed CFD-DEM model provides a valuable tool for understanding bacterial twitching in complex flow environments.
  • Environmental factors, specifically shear stress and surface topography, significantly influence bacterial twitching efficiency and distribution.
  • The findings offer fundamental insights into bacterial colonization strategies in fluid flow habitats.