Modelling the Mechanics and Hydrodynamics of Swimming E. coli

TL;DR

This study uses mesoscale hydrodynamic simulations to model the swimming mechanics of E. coli, accurately capturing flow fields and hydrodynamic coefficients consistent with experimental data.

Contribution

It introduces a detailed mesoscale simulation approach combining molecular dynamics and particle collision dynamics to model E. coli swimming behavior.

Findings

Hydrodynamic friction coefficients match experimental data.

Flow field exhibits force-dipole and vortices due to counterrotation.

Counterrotation is crucial for accurate near-field hydrodynamics.

Abstract

The swimming properties of an E. coli-type model bacterium are investigated by mesoscale hy- drodynamic simulations, combining molecular dynamics simulations of the bacterium with the multiparticle particle collision dynamics method for the embedding fluid. The bacterium is com- posed of a spherocylindrical body with attached helical flagella, built up from discrete particles for an efficient coupling with the fluid. We measure the hydrodynamic friction coefficients of the bacterium and find quantitative agreement with experimental results of swimming E. coli. The flow field of the bacterium shows a force-dipole-like pattern in the swimming plane and two vor- tices perpendicular to its swimming direction arising from counterrotation of the cell body and the flagella. By comparison with the flow field of a force dipole and rotlet dipole, we extract the force- dipole and rotlet-dipole strengths for the bacterium and find that counterrotation of the cell body and the flagella is essential for describing the near-field hydrodynamics of the bacterium.