Abstract
This study deals with the influence of a rigid surface on the motion of singly flagellated bacteria. We have developed a method to measure the distance between a cell and a surface utilizing the blurring of microscopic images out of focus, the degree of which is well quantified in terms of gradation sequence in grayscale. This method reveals the dependence of the swimming trajectory of a cell on the distance from the surface; in the range within 1.5 micrometers from the surface, most of the backwardly swimming cells draw circular trajectories, while they draw straight trajectories out of this range. Forwardly swimming cells, which draw straight trajectories near the surface, exhibit a similar tendency to the backwardly swimming ones with straight trajectories.
