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

该项目将开发一个通用的自行式微泳者模型，以了解鞭毛细菌(如大肠杆菌和鼠伤寒沙门氏菌)复杂水力学的潜在游泳机制。细菌的运动性在人类健康和医学中非常重要，因为它会导致感染的传播，包括那些因生物膜的形成而进一步复杂化的感染。这个项目将专注于解决有关细菌游动和粘性流体中的趋化行为的悬而未决的生物学问题。例如：细菌鞭毛实际上是如何捆绑和解绑的？细菌在表面附近的剪切流中的运动是如何改变的，并与细菌的致病机制有关？这个项目的目标是双重的。首先，应该建立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的比较来验证，并将用于为进一步的实验做出预测。通过对粘性流体中游动细菌的研究，可以为细菌在粘性流体中的传播和生物膜的形成提供新的信息，也可能有助于设计由鞭毛自主推进的纳米机械。本项目开发的数学方法可以建立包括杆状细胞体、旋转马达和鞭毛(柔顺钩子和柔性螺旋丝)的完整的细菌游泳者模型，从而使该模型能够同时处理细菌游泳者流体-机械相互作用的所有复杂方面。此外，数学模型生物体将按照泊松过程执行三维无偏随机游动。本项目将使用正则化Stokes公式的改进版本，结合非标准Kirchhoff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向血流变异性，这可能会影响生物医学环境中的细菌传输，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得到许多应用，其中薄薄的弹性结构和刚体与流体相互作用，包括精子运动和胃中的幽门螺杆菌等细菌病原体。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.