Motion of magnetotactic bacteria swarms in an external field

TL;DR

This paper models the motion of magnetotactic bacteria swarms under external magnetic fields, explaining their directional movement and torque production through a continuum hydrodynamic approach.

Contribution

It introduces a continuum model incorporating couple stress to quantitatively describe swarm motion and torque in response to external magnetic field tilting.

Findings

Model accurately predicts swarm directional change with field inversion.

Quantitative estimates of torque produced by bacterial rotary motors.

Describes hydrodynamically bound states of bacteria swarms.

Abstract

Magnetotactic bacteria moving on circular orbits form hydrodynamically bound states. When close to a surface and with the tilting of the field in a direction close to the perpendicular to this surface these swarms move perpendicularly to the tilting angle. We describe quantitatively this motion by a continuum model with couple stress arising from the torques produced by the rotary motors of the amphitrichous magnetotactic bacteria. The model not only correctly describes the change of direction of swarm motion while inverting the tangential field but also predicts reasonable value of the torque produced by the rotary motors.