Dynamic Model and Motion Mechanism of Magnetotactic Bacteria with Two Lateral Flagellar Bundles

Magnetotactic Bacteria (MTB) propel themselves by rotating their flagella and swim along the magnetic field lines. To analyze the motion of MTB, MTB magneto-ovoid strain MO-1 cells, each with two bundles of flagella, were taken as research object. The six-degrees-of-freedom (6-DoF) dynamic model of MO-1 was established based on the Newton Euler dynamic equations. In particular, the interaction between the flagellum and fluid was considered by the resistive force theory. The simulated motion trajectory of MTB was found to consist of two kinds of helices: small helices resulting from the imbalance of force due to flagellar rotation, and large helices arising from the different directions of the rotation axis of the cell body and the propulsion axis of the flagellum. The motion behaviours of MTB in various magnetic fields were studied, and the simulation results agree well with the experiment results. En addition, the rotation frequency of the flagella was estimated at 1100 Hz, which is consistent with the average rotation rate for Na+-driven flagellar motors. The included angle of the magnetosome chain was predicted at 40 that is located within 20 degrees to 60 degrees range of the observed results. The results indicate the correctness of the dynamic model, which may aid research on the operation and control of MTB-propelled micro-actuators. Meanwhile, the motion behaviours of MTB may inspire the development of micro-robots with new driving mechanisms.