Figure 2

Stable swimming modes of a polarly-flagellated bacterium. The helical filament is intrinsically left-handed and the cell displays four stable swimming modes as the motor rotates either CCW (a,b) or CW (c,d), and these stable swimming modes can be further classified as functions of the bending modulus of the hook (\(a^\mathrm{hook}\)) and the magnitude of applied torque (\(|\tau |\)) when the motor rotates either CCW (e) or CW (f). Different shapes of markers represent the push (\(\blacksquare\)), overwhirling (\(\bigstar\)), pull (\(\bullet\)), and wrapping (\(\blacktriangle\)) modes, and the imaginary separating lines of these marker shapes determine the critical thresholds of the applied torque, \(\tau _\mathrm{cw}\) and \(\tau _\mathrm{ccw}\). The markers (\(\varvec{-}\)) indicate that the bacterium shows neither wrapping nor pull mode for a given simulation time because the hook is too flexible and the applied torque is close to the critical value. Colors indicate the average swimming speeds measured for each mode of motility after the simulation reaches the stable steady motion.