(358c) Effects of Director Field on Dynamics of Bacteria in Liquid Crystals

Orientationally ordered liquid crystal environment is known to align the swimming direction of rod-like bacteria such as B. subtilis parallel to the local director. We present experimental studies of B. subtilis in the nematic cells with the director field that is either (i) perpendicular to the direction of swimming or (ii) contains topological defect. Perpendicular alignment (i) forces a bacterium to adopt one of the two dynamic states: (a) spinning around the longitudinal axis but not moving in the plane of the cell; (b) swimming perpendicularly to the director with hairpin-like reversals of the direction. The tumbling behavior of the bacteria adopts two modes not seen in isotropic media, namely, (1) a direct 180 degree reversal of swimming direction and (2) a random change of swimming direction through a transient spinning state. Pre-imposed topological defects (ii) allow one to control the trajectory of bacterial motion, in particular, to rectify polarity of circular orbiting and to trigger pumping. The work is supported by NSF DMR-1507637 and DMS-1434185.