Fig. 1: Nematic and polar order in thin M. xanthus layers.
a An exemplary bright field image of cells on a solid surface and the corresponding number of cell layers (see SI Fig. S2). Yellow line segments indicate the director field (cell orientations) \(\hat{{{\boldsymbol{n}}}}\), and there is a pair of +1/2 (red) and −1/2 (blue) defects in the view. The white scale bar is 10 μm. b Average director field \(\left\langle \hat{{{\boldsymbol{n}}}}\right\rangle\) around ±1/2 defects. c Mean velocity of cell flow \(\left\langle {{\boldsymbol{v}}}\right\rangle\) around +1/2 defects; the black arrows show magnitude and direction and the color map shows the speed \(\left\vert \left\langle {{\boldsymbol{v}}}\right\rangle \right\vert\). d Standard deviation \({\sigma }_{{v}_{x}}\) and \({\sigma }_{{v}_{y}}\) of the x and y components of the velocity field around +1/2 defects. The black line segments show \(\left\langle \hat{{{\boldsymbol{n}}}}\right\rangle\). e MglB proteins localize to the rear of the cell and define individual cell polarity (arrows). The kymograph shows the brightness of the fluorescent tag for one isolated moving cell (outlined by the white contours). The kymograph captures two reversal events. The white scale bar is 5 μm. f Local cell velocity vn is correlated with local polarity pn. Black circles indicate measurements in nematically aligned regions (in the black square) while red circles are for measurements in the comet tail region of +1/2 defects (in the red square). The data were measured with 7 samples and the error bars show the standard deviation. The inset is a zoom-in of the region near pn = 0. The positive direction for polarity and velocity are labeled by the thick arrows in the director field: it points toward the defect core near +1/2 defects and is left-right symmetric in aligned regions.
