Microscopic Fluid Mechanic Research for Propulsion of Bacteria with Flagella

用暗视野生物显微镜观察了溶藻弧菌（Vibrio alginolyticus）的游动运动，并用摄像机记录了其游动过程。得到了每一个细菌的胞体旋转速率与推进速度之间的线性关系。应用基于Stokes流的边界元法对单鞭毛细菌的推进进行了计算。在本研究中，我们还测量了大量溶藻弧菌的前向和后向游动速度。向后游的速度平均是向前游的1.5倍。前向游动和后向游动的速度差异可能是由电机转矩相对于旋转方向的不对称性和鞭毛丝在水动力作用下的变形等因素引起的，并对游动细菌柔性鞭毛的微小变形进行了分析。应用阻力理论估算了鞭毛所受的力。根据弹性杆的基尔霍夫模型，扭转力矩和弯曲力矩决定了变形鞭毛的曲率和扭转。在考虑鞭毛变形的情况下，模拟了前泳和后泳的速度。结果表明，前向和后向速度之间的差异不是由鞭毛的变形产生的。

The swimming motion of Vibrio alginolyticus, a bacterium with a single flagellum was observed using a dark-field biological microscope with CCD camera and was record by a video recorder. The linear relation between the rotation rate of the cell body and the propulsive speed was obtained for each individual bacterium. Computations were carried out for propulsion of the bacteria with a single flagellum applying the boundary element method based on the Stokes flow. the comparison is well between the observations and the simulations.In the present investigation, the forward and backward swimming speeds were also measured for a lot of Vibrio alginolyticus. The speed of backward swimming is 1.5 times larger than that of forward swimming on average. The difference of the speed between the forward and the backward swimming might be caused by several factors such as asymmetry of the motor torque with respect to the rotational direction and deformation of the flagellum filament due to hydrodynamic forces.An analysis was conducted for the small deformation of flexible flagellum of swimming bacteria. The resistive force theory was applied to estimate the force exerted on flagellum. The torsional as well as the bending moments determine the curvature and the torsion of the deformed flagellum according to the Kirchhoff model for elastic rod. The speeds were simulated for the forward and the backward swimming taking account of deformation of flagellum. It is shown that the difference between the forward and the backward speeds is not generated by the deformation of the flagellum.