Directional Swimming of B. Subtilis Bacteria Near a Switchable Polar Surface

The dynamics of swimming bacteria depend on the properties of their habitat media. Recently it is shown that the motion of swimming bacteria dispersed directly in a non-toxic water-based lyotropic chromonic liquid crystal can be controlled by the director field of the liquid crystal. Here, we investigate whether the macroscopic polar order of a ferroelectric nematic liquid crystal (N_F) can be recognized by bacteria B. Subtilis swimming in a water dispersion adjacent to a glassy N_F film by surface interactions alone. Our results show that B. Subtilis tends to move in the direction antiparallel to the spontaneous electric polarization at the N_F surface. Their speed is found to be the same with or without a polar N_F layer. In contrast to observation on crystal ferroelectric films, the bacteria do not get immobilized. These observations may offer a pathway to creation of polar microinserts to direct bacterial motion in vivo.