Collaborative Research: Effects of Fluid Flow on Flagellar Mechanics and Microbial Motility

浮游生物、精子和细菌等游动细胞在环境、人类健康和工业系统中发挥着至关重要的作用。这些细胞分解污染物和废物，在繁殖过程中运输DNA，并提供了一种有前途的可再生生物燃料来源。游泳是许多单细胞的基本策略，它们利用毛发状的鞭毛向营养物质和配偶游去，远离毒素。然而，有时细胞必须？游上游吗?克服无处不在的水流和它们游泳的环境流体。流体流动在鞭毛力学和细胞自发运动中的作用尚不清楚。这个研究项目是通过直接成像和数学建模的结合来研究流体流动如何改变鞭毛运动。这项工作对医疗设备和医疗的发展、生物反应器和生物燃料生产效率的提高以及海洋、湖泊和地下水生态系统动力学的理解具有广泛的意义。众所周知，环境速度梯度会导致以高剪切速率为特征的流动区域的细胞强烈积聚，而细胞积聚的性质强烈依赖于细胞的运动性、形状和鞭毛。本研究项目采用微流体、高速成像和最先进的数值模拟相结合的协同方法：(1)确定流动对单个系住细胞鞭毛跳动的流体动力学影响；(2)确定外界施加的水流如何通过鞭毛变形影响自由游动细胞的流体力学和运输；(3)确定鞭毛力学如何与活跃细胞密集悬浮液中集体、自生流动耦合。该项目在单细胞流体动力学领域开辟了一个新的、丰富的研究方向，流体流动的作用在很大程度上被忽视，尽管它在生物学、生态学和医学方面具有许多意义。该项目的研究人员正在建立独特的经验数据集和数值模型，以绘制外部流体力对鞭毛内主动力产生的影响，这些信息将成为微生物学家，生态学家和对细胞运动建模感兴趣的生物物理学家的资产。该项目还扩展了现有的方法，通过表征具有内力产生的柔性附属物（即鞭毛）的变形来量化流动-结构相互作用。本项目支持的研究生和本科生在流体动力学和微生物生物物理学方面接受独特的跨学科培训。印第安纳州立博物馆的一个动手高速成像互动展览结合了这些研究主题，将向参观博物馆的中学生开放。

Swimming cells including plankton, sperm, and bacteria play a crucial role in the environment, in human health, and in industrial systems. These cells breakdown pollutants and waste products, transport DNA during reproduction, and provide a promising source of renewable biofuel. Swimming is a fundamental strategy of many single cells, which use hair-like flagella to swim toward nutrients and mates, and away from toxins. However, sometimes cells must ?swim upstream?, and overcome ubiquitous currents and ambient flow of the fluid in which they swim. The role of fluid flow on flagellar mechanics and the spontaneous movement of cells is not well understood. This research project is studying how fluid flow modifies flagellar motion through a combination of direct imaging and mathematical modeling. This work has broad implications for the development of medical devices and medical treatments, the improvement of bioreactors and biofuel production efficiency, and understanding ecosystem dynamics in oceans, lakes, and groundwater. Ambient velocity gradients are known to lead to strong accumulations of cells in flow regions characterized by high shear rates, and the nature of the cell accumulation is strongly dependent on cell motility, shape, and flagellation. This research project uses a synergistic approach incorporating microfluidics and high-speed imaging with state-of-the-art numerical simulations to: (1) Determine the hydrodynamic effects of flow on the flagellar beating of single, tethered cells; (2) Determine how externally-imposed flow affects the hydrodynamics and transport of free swimming cells through flagellar deformation; (3) Establish how flagellar mechanics couple to collective, self-generated flows in dense suspensions of active cells. This project is opening a new, rich research direction in single cell hydrodynamics, where the role of fluid flow has been largely neglected, despite its many implications for biology, ecology and medicine. The researchers on this project are establishing unique empirical data sets and numerical models that map the effects of external fluid forces on active force generation inside flagella, and such information will be an asset to microbiologists, ecologists, and biophysicists interested in modeling cell locomotion. The project is also extending existing methods to quantify flow-structure interactions by characterizing the deformation of flexible appendages having internal force generation, i.e. flagella. Graduate and undergraduate students supported by this project are receiving unique interdisciplinary training in fluid dynamics and microbial biophysics. A hands-on high-speed imaging interactive exhibit at the Indiana State Museum is incorporating these research themes, which will reach middle school students who attend the museum.