Fluid-mechanical Interaction of a Bacterial Swimmer with Flagella and Bacterial Chemotaxis

该项目将开发一种自推进微型游泳器的多功能模型，以了解鞭毛细菌（如大肠杆菌和鼠伤寒沙门氏菌）复杂流体动力学的潜在游泳机制。细菌运动性在人类健康和医学中非常重要，因为它导致感染的传播，包括那些因生物膜形成而进一步复杂化的感染。这个项目将集中在解决未回答的生物学问题，细菌游泳和趋化行为在粘性流体。例如：细菌鞭毛实际上是如何捆绑和解开的？在表面附近的剪切流中细菌运动性是如何改变的以及与细菌发病机制的关系？这个项目的目标是双重的。首先，应开发出符合生物学的细菌游泳者的数学模型。其次，这些模型将通过与实验数据进行比较来验证，并将用于为进一步的实验做出预测。从这项关于粘性流体中自由游动细菌的研究中获得的结果可能会提供有关感染传播和生物膜形成的新信息，也可能有助于设计由鞭毛自推进的纳米机器。该项目中开发的数学方法能够构建细菌游动者的完整模型，包括杆状细胞体，旋转电机，和鞭毛（一个顺应钩和灵活的螺旋丝），使模型可以同时处理所有复杂的方面的流体机械相互作用的细菌游泳。此外，数学模型有机体将执行一个三维无偏随机行走以下泊松过程。该项目将使用正则化斯托克斯公式的改进版本，结合非标准基尔霍夫杆理论和中性浮力刚性细胞体动力学，以描述细胞模型的流体-机械相互作用。 该模型还将用于研究表面附近的正趋流性，这可能会影响生物医学环境中的细菌运输，如尿路和导管。在这个项目中开发的方法和工具将在生物流体中找到许多应用，其中薄的弹性结构与刚性体一起与流体相互作用，包括精子运动和细菌病原体，如H。该奖项反映了NSF的法定使命，并被认为是值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估的支持。

This project will develop a versatile model of a self-propelled microswimmer to understand the underlying swimming mechanisms of the complex hydrodynamics of flagellated bacteria such as Escherichia coli and Salmonella typhimurium. Bacterial motility is profoundly important in human health and medicine, as it results in the spread of infections, including those further complicated by biofilm formation. This project will focus on addressing unanswered biological questions about bacterial swimming and the chemotactic behavior in viscous fluids. For example: How do bacterial flagella actually bundle and unbundle? How is bacterial motility in shear flow near surfaces modified and related to bacterial pathogenesis? The goal of this project is twofold. First, mathematical models of bacterial swimmers that are true to biology shall be developed. Second, these models will be validated by comparing them to experimental data, and will be used to make predictions for further experiments. The results obtained from this research on free swimming bacteria in viscous fluids may provide new information about the spread of infections and biofilm formation, and may also help to design nanomachines that are self-propelled by flagella.The mathematical method developed in this project enables to build a complete model of a bacterial swimmer that includes a rod-shaped cell body, rotary motors, and flagella (a compliant hook and a flexible helical filament) so that the model can deal simultaneously with all complex aspects of the fluid-mechanical interaction of the bacterial swimmer. In addition, the mathematical model organism will execute a three-dimensional unbiased random walk following Poisson process. This project will use an improved version of the regularized Stokes formulation combined with the nonstandard Kirchhoff rod theory and the neutrally buoyant rigid cell body dynamics in order to describe the fluid-mechanical interaction of the cell model. This model will also be used to investigate positive rheotaxis near a surface, which can affect bacterial transport in biomedical settings such as the urinary tract and catheters. The methods and tools developed in this project will find many applications in biological fluids, where thin elastic structures together with rigid bodies interact with fluids, including sperm motility and bacterial pathogens such as H. pylori in the stomach.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.