Abstract

Magnetotactic bacteria are prokaryotic micro-swimmers characterised by their ability to synthetize chains of nano-magnets in their cytoplasm, magnetosomes. They passively align to magnetic lines through magnetic torque, which enables them to be easily controlled remotely. We use microfluidics experiments to explore the self organisation and unsteady dynamics of magnetotactic bacteria AMB1 . A uniform distribution of bacteria under confinement is rendered unstable by the application of a magnetic field perpendicular to channel walls. A state of bacterial magneto-convection results wherein bacterial plumes emerge spontaneously perpendicular to the wall and develop into stable and reproducible self-sustained flow convection cells. Using a theoretical model based on hydrodynamic singularities, we reproduce reproduce the flow field in the bacteria suspension and capture quantitatively the instability as well as the observed long-time growth and merging of the plumes.