Dynamics of Motile Flagella in Fluid Media

About This Grant

Abstract Flagella—motile, hair-like appendages extending from the surface of cells—are ubiquitously present across all three domains of life. These organelles carry out diverse functions of cells, including motility, sensory perception, and fluid transport, through their primary ability to move ambient fluids relative to the cells. Thus, understanding the interaction between flagella and their surrounding fluid, particularly their fluid-transport capability, is crucial to addressing a wide range of fundamental biological questions. While advances in electron microscopy and X-ray crystallography have illuminated the ultrastructures of bacterial and eukaryotic flagella, the dynamics of motile flagella in fluid environments remain poorly understood. The challenges in studying flagellar dynamics in fluid media stem from the lack of suitable experimental tools capable of imaging collective flagellar motions in real time at small length scales and mapping the three-dimensional (3D) fluid flow around rapidly beating flagella with high spatial and temporal resolution. Drawing on my unique training and career path, I lead a research group that develops new physical model systems and advanced novel imaging techniques to elucidate fluid-mediated flagellar dynamics in key biological processes. Specifically, we aim to address two critical questions on flagellar dynamics in this R35 MIRA proposal. 1) Resolving the synchronized dynamics of prokaryotic flagella that enable the formation of a bacterial flagellar bundle, a process essential for bacterial motility and chemotaxis. 2) Imaging the 3D fluid flow generated by beating eukaryotic flagella and their various mutants, a long-standing challenge that is central to the understanding of the functional consequences of normal and dysfunctional flagella and the key step towards the development of treatments for ciliopathies. Specifically, in Goal 1 of our proposed research, we will integrate experiments on peritrichous bacteria Escherichia coli and their genetically engineered mutants with a scaled physical model of a bacterial flagellar bundle constructed in my lab. This unique approach will help to reveal the detailed mechanisms, through which different physical factors, such as hydrodynamic interactions, the elastic properties of flagellar hooks, and motor torque fluctuations, control the synchronization and formation of bacterial flagellar bundles. In Goal 2, we will develop a new imaging technique—high-speed tracking holographic microscopy—to measure the temporal variations of the three-dimensional flow around the beating flagella of a green alga, Chlamydomonas reinhardtii, which serves as a premier model for eukaryotic flagella. Our research will deliver the first comprehensive characterization of the 3D flow field generated by isolated motile eukaryotic flagella in their natural, unperturbed state and directly correlate abnormal flagellar structures with their functional deficiencies in fluid transport. Thus, through the innovative model system and the advanced experimental techniques pioneered in our lab, our study will address crucial open questions on the dynamics of motile prokaryotic and eukaryotic flagella in fluid media.