Biased locomotion is a common feature of microorganisms, but little is known about its impact on self-organisation. Inspired by recent experiments showing a transition to large-scale flows, we study theoretically the dynamics of magnetotactic bacteria confined to a drop. We reveal two symmetry-breaking mechanisms (one local chiral and one global achiral) leading to self-organisation into global vortices and a net torque exerted on the drop. The collective behaviour is ultimately controlled by the swimmers' microscopic chirality and, strikingly, the system can exhibit oscillations and memory-like features.
@article{arxiv.2312.03158,
title = {Controlling confined collective organisation with taxis},
author = {Albane Théry and Alexander Chamolly and Eric Lauga},
journal= {arXiv preprint arXiv:2312.03158},
year = {2023}
}