Magnetic response of Magnetospirillum gryphiswaldense observed inside a microfluidic channel

Highlights: • Magneto-tactic bacteria swim along magnetic field lines. • Response is governed by a balance between magnetic and rotational drag torque. • Rotational velocity is linear with magnetic fields up to 10 mT. • The spiral shaped body needs to be considered for rotational drag. In this study we modelled and measured the U-turn trajectories of individual magnetotactic bacteria under the application of rotating magnetic fields, ranging in amplitude from 1 to 12 mT. The model is based on the balance between rotational drag and magnetic torque. For accurate verification of this model, bacteria were observed inside 5 μm tall microfluidic channels, so that they remained in focus during the entire trajectory. From the analysis of hundreds of trajectories and accurate measurements of bacteria and magnetosome chain dimensions, we confirmed that the model is correct within measurement error. The resulting average rate of rotation of Magnetospirillum gryphiswaldense is 0.74 ± 0.03 rad/mTs.