Motion reversal in Living Liquid Crystals

The term Living Liquid Crystal has been adopted for active systems combining swimming bacteria with a lyotropic liquid crystal. Such systems exhibit novel phenomena resulting from the coupling between the swimming activity of bacteria and long-range orientational order of a liquid crystal. Under these conditions, the bacteria have been observed to follow the nematic director and accumulate or deplete in the topological defects, depending on their nature. In such a system, a classical run-and-tumble picture of bacterial motility is replaced by motion reversals. Here we describe the motion reversal of common bacteria Bacillus subtilis along a 1D path determined by the director. The reversals are understood in terms of the flagellar dynamics in an anisotropic fluid. The filaments are directly visualized allowing for a qualitative understanding of the emergent phenomena and quantification of the individual flagellar contributions to the motion of the entire bacterium.