Directional Swimming of B. subtilis Bacteria Near the Surface of Ferroelectric Nematic Liquid Crystal Films

Controlling the motion of bacteria by volume interactions in lyotropic chromonic nematic liquid crystal environments was studied widely in the past decade ¹. The goal of this study was to find out whether the motion of bacteria can be guided by surface interactions. For this we chose a recently discovered ferroelectric nematic liquid crystal (FNLC) which is glassy at room temperature ^2,3. We put a drop of bacteria in terrific broth on a film of aligned FNLC and found that bacteria tend to align preferably opposite to the polarization direction of the FNLC. Interestingly, that direction of the polarization of FNLC can be set by applying electric fields or by using surface alignments prior to applying bacteria. This effect can be explained by the highly charged surface of bacteria and the potassium ion concentration gradient in the medium induced by the depolarization field of the underlying FNLC film.