Studying Bacterial Swimming, One Cell at a Time

本项目的重点是在光阱中测量游动细菌，以研究细菌推进的基本特性。 该项目的一个特定目标是确定细菌鞭毛（或其束）的结构与推进矩阵之间的关系，该关系将鞭毛的平移和旋转速度与推动细菌的扭矩和力联系起来。一旦推进矩阵是已知的，动力学特性，如力，扭矩，游泳速度，功率和游泳效率可以从电机的角速度的测量获得。 初步的测量结果显示出有希望的结果，本文提出的研究试图通过将测量的推进矩阵元素与使用螺旋线圈作为模型鞭毛的计算进行比较来引导实验进入下一步。该项目还将通过捕获两种彼此靠近的细菌来解决鞭毛捆绑和非捆绑过渡的问题。考虑到细菌细胞体和鞭毛的大小，预计热噪声将对推进装置的性能产生影响。噪声将通过检查扭矩和推力的波动以及由此产生的细菌轨迹来研究。这项研究的一个重要部分是教育和培训学生在一个领域，这是非常有吸引力的学生，因为潜在的生物/物理现象是耐人寻味的，数学理论是具有挑战性的和美丽的。

This project focuses on measurements of swimming bacteria in optical traps in order to study the fundamental properties of bacterial propulsion. A particular goal of the project is to determine the relationship between the structures of bacterial flagellum (or its bundles) and the propulsion matrix, which relates the translational and the rotational velocities of the flagellum to the torque and the force propelling the bacterium. Once the propulsion matrix is known, dynamical properties such as forces, torques, swimming speed, power, and swimming efficiency can be obtained from measurements of the angular velocity of the motor. Preliminary measurements have shown promising results, and the proposed research herein attempts to lead the experiment to the next step by comparing the measured propulsion matrix elements with calculations using helix coils as a model flagellum. The project will also address the issue of flagellar bundling and unbundling transitions by trapping two bacteria in close proximity to each other. Given the size of the bacterial cell body and the flagellum, it is expected that thermal noise will have an effect on the performance of the propulsion apparatus. The noise will be studied by examining fluctuations in the torque and thrust, and the resulting bacterial trajectories. A significant part of this research is to educate and train students in an area that is very attractive to students because the underlying biological/physical phenomena are intriguing and the mathematical theory is challenging and beautiful.