Magnets Make Bacteria Flow

In the December 2025 issue of Physical Review Letters, Dr. Damien Faivre, in collaboration with colleagues from Lyon, France, reports an advance in the control of active matter with their article “Driven Shear Flow in Biological Magnetoactive Fluids.” 

Using magnetotactic bacteria, organisms that respond simultaneously to chemical and magnetic cues, the study demonstrates how external fields can orchestrate individual swimmer dynamics into global shear flows. 

By shaping both positional and orientational order, the collective force dipoles of the bacteria generate a finite active stress, quantitatively captured by a magnetoactive fluid model. Beyond steady-state behavior, the work reveals rich, time-dependent responses under rotating magnetic fields, opening new perspectives on steering active biological systems for both fundamental and applied purposes.