Hydrodynamics of bacterial spinning top

We have theoretically and numerically investigated mono-flagellated bacterial swimming dynamics near a wall boundary with considering elastic hook flexibility to understand hydrodynamic interactions underlying the bacterial upright spinning motion, which has referred as ‘low-Reynolds-number spinning top’ in a recent experimental study. We establish an elastohydrodynamic stability theory and found that the vertical spinning motion is enabled by the mechanical competition between the destabilization by the flagellar propulsion and rotational stabilization by the elastic coupling of the hook. These results demonstrate the mechanical nature of the behaviours in rich diversity and could contribute to our deeper understandings of the bacterial surface motility and biofilm formation.