Life in Suspense: Particle dynamics in suspensions of swimming bacteria by Alison E. Patteson
Host: Prof. Lisa Manning/ Contact: Yudaisy Salomón Sargentón, 315-443-5960
202 Physics Bldg.
Cells and microorganisms move in diverse environments that range from simple pond and ocean water to complex biological fluids, such as mucus. These environments frequently contain passive particles, such as macromolecules, flexible polymers, or colloids, which can influence cell motility and function. Interactions between cells and particles underlie many aspects of medicine, biology, and engineering, including the spread of bacterial infections, the formation of biofilms, and the design of swimming micro-robots. I use particles (1-10 micron) and polymer molecules (<1 micron) to experimentally investigate particle-bacteria interactions in suspensions of swimming Escherichia coli. By varying the size of passive spherical particles, I find an anomalous diffusive regime in E. coli suspensions, in which larger particles diffuse faster than smaller particles. This feature arises due to an interplay between the particle’s Brownian diffusion and convection through bacterial interactions. When flexible polymers are added to the suspending fluid, the E. coli drastically change their swimming behavior: cells swim faster and tumble less often, drastically enhancing their translational diffusion. By varying polymer molecular weight, I find that fluid viscosity suppresses cell tumbling while fluid elasticity increases swimming speed. I demonstrate that E. coli produce elastic stresses in the fluid by visualizing fluorescently-labeled DNA polymers, which deform and stretch under the applied flows generated by a single E. coli. Together these results uncover new avenues of transport in active fluids, which can be used to control the spread of bacteria or the dispersion of particles in microbial environments. I discuss applications to particle sedimentation and explore how crawling mammalian cells move through and interact with small tissue-like pores.