Mushenheim Peter C, Trivedi Rishi R, Roy Susmit Singha, Arnold Michael S, Weibel Douglas B, Abbott Nicholas L
Department of Chemical and Biological Engineering, University of Wisconsin-Madison, 1415 Engineering Drive, Madison, WI 53706, USA.
Soft Matter. 2015 Sep 14;11(34):6821-31. doi: 10.1039/c5sm01489a. Epub 2015 Jul 30.
We report on the organization and dynamics of bacteria (Proteus mirabilis) dispersed within lyotropic liquid crystal (LC) films confined by pairs of surfaces that induce homeotropic (perpendicular) or hybrid (homeotropic and parallel orientations at each surface) anchoring of the LC. By using motile vegetative bacteria (3 µm in length) and homeotropically aligned LC films with thicknesses that exceed the length of the rod-shaped cells, a key finding reported in this paper is that elastic torques generated by the LC are sufficiently large to overcome wall-induced hydrodynamic torques acting on the cells, thus leading to LC-guided bacterial motion near surfaces that orient LCs. This result extends to bacteria within LC films with hybrid anchoring, and leads to the observation that asymmetric strain within a hybrid aligned LC rectifies motions of motile cells. In contrast, when the LC film thickness is sufficiently small that confinement prevents alignment of the bacteria cells along a homeotropically aligned LC director (achieved using swarm cells of length 10-60 µm), the bacterial cells propel in directions orthogonal to the director, generating transient distortions in the LC that have striking "comet-like" optical signatures. In this limit, for hybrid LC films, we find LC elastic stresses deform the bodies of swarm cells into bent configurations that follow the LC director, thus unmasking a coupling between bacterial shape and LC strain. Overall, these results provide new insight into the influence of surface-oriented LCs on dynamical bacterial behaviors and hint at novel ways to manipulate bacteria using confined LC phases that are not possible in isotropic solutions.
我们报告了分散在由诱导溶致液晶（LC）垂直（垂直）或混合（每个表面垂直和平行取向）锚定的成对表面所限制的溶致液晶（LC）薄膜内的细菌（奇异变形杆菌）的组织和动力学。通过使用运动性营养细菌（长度为3微米）和厚度超过杆状细胞长度的垂直排列的LC薄膜，本文报道的一个关键发现是，LC产生的弹性扭矩足够大，足以克服作用在细胞上的壁诱导流体动力扭矩，从而导致在使LC取向的表面附近的LC引导细菌运动。这一结果扩展到具有混合锚定的LC薄膜中的细菌，并导致观察到混合排列的LC内的不对称应变纠正了运动细胞的运动。相比之下，当LC薄膜厚度足够小以至于限制阻止细菌细胞沿垂直排列的LC指向矢排列时（使用长度为10 - 60微米的群体细胞实现），细菌细胞沿与指向矢正交的方向推进，在LC中产生具有显著“彗星状”光学特征的瞬态畸变。在此极限下，对于混合LC薄膜，我们发现LC弹性应力将群体细胞体变形为遵循LC指向矢的弯曲构型，从而揭示了细菌形状与LC应变之间的耦合。总体而言，这些结果为表面取向的LC对细菌动力学行为的影响提供了新的见解，并暗示了利用在各向同性溶液中不可能的受限LC相来操纵细菌的新方法。
