Pushing & Pulling, Bending & Buckling; Viscosity and Elasticity in Flagellar Swimming

Breuer，Kenny 1336638本研究的目的是观察和跟踪单个细菌，以阐明琼脂运动的物理机制。这项研究的核心工具是数字跟踪显微镜（DTM），它可以跟踪单个细胞任意长的时间。该项目的第一阶段是改进已经以原型形式存在的DTM。一旦完成，DTM将被部署以测量单个游泳细胞在几分钟内的速度和方向。这些测量将产生单个细菌细胞（如C。crescentus、E. coli和S. marascens。通过将游泳速度和细胞取向与细胞的几何特性（如细胞形状、凝胶长度和凝胶数量）相关联，并通过使用理论和计算来确定作用于细胞的流体和弹性应力，PI将阐明物理约束如何决定游泳行为。斯托克斯流动分析将与弹性理论相结合，通过这种综合，PI将解释为什么处于“推动者”模式的细胞，在游动细胞后面的凝胶，比处于“拉动者”模式的细胞移动得更快，在游动细胞前面的凝胶。悬浮液的流变性对游泳行为的影响也将被探讨。大多数感染性细菌在进入人体时会遇到粘液（一种非牛顿流体），因此PI将跟踪非牛顿流体中的游动细菌。智力优势：这项工作的智力优势在于DTM允许大量新的测量和观察。通过观察单个细菌细胞随时间的变化，可以研究群体中个体变异的影响。对单个细胞的追踪已经在C.新月形，如推和拉之间的游泳速度的差异。DTM的高分辨率推动了更复杂的定量理论的发展，这些理论将流体力学与材料特性和弹性相结合，并且可以与我们的精确测量进行比较。虽然近年来已经看到积极关注理想化的理论方法和桌面模型的游泳，拟议的工作承诺一个新的水平的细节，从活细胞研究，以前没有可能。更广泛的影响：PI将参与外展和招聘活动。co-PI将继续参与教师研究经验计划，该计划邀请当地学校的K-12教师到布朗校园参加夏季实验室研究和课程开发项目，并参加布朗大学夏季高中计划，就运动物理学进行讲座和演示。PI还将为普罗维登斯课后联盟（PASA）提供讲座和讨论。PASA是一个当地组织，通过以科学为导向的项目为高中生提供更多的学习机会。最后，合作还将开发基于网络的教育媒体，以说明细菌运动，琼脂运动，显微镜和PIV的概念。

Breuer, Kenny 1336638The goal of this research is to observe and track individual bacteria in order to elucidate the physical mechanisms of agellar motility. The central tool of the study is a Digital Tracking Microscope (DTM), which allows tracking of a single cell for arbitrarily long times. The first stage of the project is the refinement of the DTM, which already exists in prototype form. Once completed the DTM will be deployed to measure the velocity and orientation of single swimming cells over the course of several minutes. These measurements will yield detailed statistics for the swimming behavior of single bacterial cells such as C. crescentus, E. coli, and S. marascens. By correlating the swimming velocity and cell orientation with geometrical properties of the cell, such as cell shape, agellum length, and number of agella, and by using theory and computation to determine the fluid and elastic stresses acting on the cell, the PIs will elucidate how physical constraints determine swimming behavior. Stokes flow analysis will be coupled with elasticity theory in a combined manner, and with this synthesis, the PIs will explain why cells in 'pusher' mode, with the agellum behind the swimming cell, move faster than cells in 'puller' mode, with the agellum ahead of the swimming cell. The effects of the rheology of the suspending fluid on the swimming behavior will also be explored. Motivated by the fact that most infectious bacteria encounter mucus, a non-Newtonian fluid, when they enter the body, the PIs will track swimming bacteria in non-Newtonian fluids.Intellectual Merit :The intellectual merit of this work is that the DTM allows a host of new measurements and observations. By observing single bacterial cells over time, it becomes possible to study the effects of individual variation across a population. Tracking of individual cells has already lead to new discoveries in C. crescentus, such as the difference in swimming speed between pushers and pullers. The high resolution of the DTM motivates the development of more sophisticated quantitative theories that integrate fluid mechanics with material properties and elasticity, and can be compared with our precise measurements. While recent years have seen active focus on idealized theoretical approaches and table-top models for swimming, the proposed work promises a new level of detail from live cell studies that have not previously been possible.Broader Impacts :The PIs will participate in outreach and recruitment activities. The co-PIs will continue to participate in the Research Experiences for Teachers program, which invites K-12 teachers from local schools to the Brown campus to participate in laboratory research and course development projects during the summer, and in the Brown University Summer High School program, giving lectures and demonstrations on the physics of locomotion. The PIs will also contribute lectures and discussions to the Providence After School Alliance (PASA) - a local organization that provides expanded learning opportunities to high-school students through science-oriented programs. Lastly, the collaboration will also develop web-based educational media to illustrate the concepts of bacterial motility, agellar motion, microscopy, and PIV.