Swimming microbes mediate important natural and engineering processes, including biogeochemical cycles, disease transmission, and bioremediation. The function of motile cells relies on their ability to reorient their swimming direction toward favorable conditions in habitats ranging from saturated soils and sediments to the tissues of host organisms. However, such complex physical environments are often characterized by intricate porous microstructure, dynamic fluid flows, and heterogeneous rheological properties, which can severely impact cell transport. First, focusing on bacterial motility in porous media, we use microfluidic experiments to disentangle the effects of pore geometry, flow, and directional swimming cues. In quiescent porous environments, successive scattering events from solid surfaces rapidly decorrelate the random walks of bacteria, but in contrast, ambient fluid flows align cells in the ow direction and anisotropically enhance dispersion. In the case of magnetotactic bacteria, upstream cell alignment to an external magnetic field reveals a novel hydrodynamic trapping mechanism that localizes cells in pores over a broad range of ow conditions. In the second part of the talk, we consider cell motility in a viscosity gradient, a common scenario in mucus layers and biofilms. We show that biflagellated microalgae exhibit a striking viscophobic turning motility, which stems from a flagellar thrust imbalance and causes unexpected cell accumulation in low viscosity zones. Taken together, these studies illustrate a bevy of microscopic physical mechanisms that can inhibit or enhance the macroscopic transport properties of swimming cells and ultimately, their function and productivity in their environments.
About the Speaker
Dr. Jeffrey S. Guasto is an associate professor in the Department of Mechanical Engineering at Tufts University. He received both a B.S. in Mechanical Engineering and a B.S. in Physics from Lehigh University in 2003. Subsequently, Prof. Guasto earned his Sc.M. and Ph.D. in Mechanical Engineering from Brown University in 2008, where he studied interfacial colloidal dynamics and fluid slip in microfluidic channels. He was a postdoctoral research associate in the Physics Department at Haverford College from 2008 to 2010 and later, a postdoc in the Department of Civil and Environmental Engineering at MIT from 2010 to 2013, where he developed an interest in the bio-fluid dynamics and transport of swimming cells. Prof. Guasto has been a member of the faculty at Tufts University since 2013, where he also holds an adjunct appointment in the Department of Physics and Astronomy. He teaches courses on fluid mechanics, transport, thermodynamics, and microfluidics. His current research interests are focused on the transport of swimming cells and active matter, flagellar mechanics, porous media and complex fluid flows, and microfluidics. In 2016, Prof. Guasto received a National Science Foundation CAREER Award for his work on elucidating the transport of swimming cells in complex environments.
Host: Professor Gabriel Juarez