Abstract
To elucidate the characteristics of flow in the collective motion of bacteria, we performed microscopic observation of the cells cultured on a semi-fluid medium. The collective motion occurs when the average cell-cell distance decreases to 5 μm, almost the same as the size of the cell. The standard deviation of the angle between velocity vectors represents the degree of collective motion well. The characteristic size of the swarming group is deduced by the analysis of the correlation with respect to the direction parallel and perpendicular to the swimming direction; 30 μm in length and 10 μm in width.
