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

这项研究的目的是观察和跟踪单个细菌，以阐明细胞运动的物理机制。这项研究的中心工具是数字跟踪显微镜(DTM)，它可以对单个细胞进行任意长时间的跟踪。该项目的第一阶段是对DTM的改进，该DTM已经以原型形式存在。一旦完成，DTM将被部署来测量几分钟内单个游泳单元的速度和方向。这些测量将产生单个细菌细胞游泳行为的详细统计数据，如新月弯孢杆菌、大肠杆菌和海马斯氏杆菌。通过将游泳速度和细胞取向与细胞的几何性质(如细胞形状、凝胶长度和Agella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以一种结合的方式与弹性理论相结合，通过这种合成，PI将解释为什么处于‘Pusher’模式的细胞移动得比处于‘Puller’模式的细胞更快，而agellum在游动细胞的前面。还将探讨悬浮液的流变性对游泳行为的影响。由于大多数传染性细菌在进入人体时会遇到粘液，这是一种非牛顿流体，PI将跟踪非牛顿流体中的游泳细菌。智力价值：这项工作的智力价值在于DTM允许许多新的测量和观察。通过观察单个细菌细胞随时间的变化，可以研究种群中个体差异的影响。对单个细胞的追踪已经导致了对新月藻的新发现，例如推进者和牵引者之间的游泳速度差异。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，可以与我们的精确测量进行比较。虽然近年来人们积极关注游泳的理想化理论方法和桌面模型，但拟议的工作承诺将活细胞研究的细节提高到一个新的水平，这是以前无法实现的。更广泛的影响：PI将参与外展和招募活动。联合PIS将继续参与教师研究体验计划，该计划邀请当地学校的K-12教师在暑期到布朗校园参加实验室研究和课程开发项目，并参加布朗大学暑期高中计划，就运动物理学进行讲座和演示。PIS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计划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、银核运动、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.