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.