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

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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.