Driven shear flow in biological magneto-active fluids

Active fluids made of powered suspended particles have unique abilities to self-generate flow and density structures. How such dynamics can be triggered and leveraged by external cues is a key question of both biological and applied relevance. Here we use magnetotactic bacteria to explore how chemotaxis and magnetotaxis -- leading, respectively, to positional and orientational responses -- combine to generate global scale flows. Such steady regime can be quantitatively captured by a magneto-active hydrodynamic model, while time-dependent magnetic driving unveils additional patterning complexity. Overall, our findings shed light on how active fluids respond to the ubiquitous situation of multiple external information, also suggesting routes for their manipulation.