Collaborative research: The effects of fluid flow on flagellar mechanics and microbial motility

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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.