Microscopic Fluid Dynamic Research for Locomotion of Bacterium with Flagella

本文应用阻力理论、边界元方法、Stokes流细长体理论等分析方法，分析了细菌在水中的运动规律，并用暗场生物显微镜观察了溶藻弧菌的游动过程，并用盒式录像机进行了记录。假设细菌由球形或球形细胞体和刚性螺旋鞭毛组成，根据阻力理论推导了细菌旋转鞭毛的运动公式。数值算例表明，根据细胞表面鞭毛的形状，细菌的运动轨迹遵循单螺旋、双螺旋和错位螺旋的几种模式，并应用边界元方法和Stokes流的细长体理论开发了计算程序来计算细菌的运动。基于边界元的计算方法计算精度最高，但计算时间较长。利用带CCD摄像机的暗场生物显微镜和录像机，观察了单鞭毛细菌溶藻弧菌的游泳运动。细菌游之字形的图像是手动跟踪的。根据视频数据测量细胞体的游泳速度和自转速度。由观测得到了细胞体转速与速度之间的线性关系，并将观测到的关系与边界元方法得到的细菌形状参数的结果进行了比较。他们之间的协议很好。这一事实得出结论，在低雷诺数下，单鞭毛细菌的运动机制可用流体动力学很好地描述。

In the present investigation, the locomotion of bacteria in water is not only analyzed applying several analytical approaches such as the resistive force theory, the boundary element method, and the slender body theory for Stokes flows, but also the swimming of Vibrio alginolyticus is observed using a dark-field biological microscope and is recorded by a video cassette recorder. The results of observation is compared with the analytical results.Formulations based on the resistive force theory are performed for motion of bacteria with rotating flagella assuming that a bacterium consists of a spherical or spheroidal cell body and rigid helical flagella. Numerical examples show that the trajectory of the bacterium follows several patterns of helix such as a single, a double and a disorted helix according to configuration of the flagelum located on the cell surface.Computational procedures are also developed to calculate locomotion of the bacteria by applying the boundary element method (BEM) as well as the slender body theory for Stokes flow. The computational method based on BEM is most accurate but needs expensive computation time.The swimming motion of Vibrio alginolyticus, a kind of monotrishously flagellated bacteria is observed using a dark-field biological microscope with CCD camera as well as a video cassette recorder. The image of the bacteria swimming zigzag is tracked manually. The swimming speed and rotation rate of the cell body are measured from the video data. Linear relations between the speed and the rotation rate of the cell body are obtained from the observation.The observed relations are compared with those obtained from results of BEM for shape parameters of the observed bacteria. The agreement is very good between them. This fact leads to the conclusion that the mechanism of locomotion of monotrishously flagellated bacteria is well described by fluid dynamics at low Reynolds number.