Event

Soft matter, a term not used often a few decades ago, has become a recognized branch of physics studied by researchers worldwide from multiple disciplines. My own random walk in this field started with experiments on filamentous viruses to study their behavior to form liquid crystalline phases, and then on protein filaments such as F-actin and microtubules to understand what drive their lateral aggregation, droplet formation, and dynamic patterns, and over the last decade, on a form of bacterial collective motility called swarming. I have gradually recognized that these happen to be a few good examples of soft matter systems of biological origin. Research in any of these systems must be conducted in tune with the cultures and applications of both soft matter and biological sciences.

A prevalent form of bacterial collective motility, called swarming, occurs in a range of physiological settings, such as on human airway and intestinal epithelia. Our ongoing study focuses on a particular species of bacteria, the Enterobacter sp. SM3, which manifests strong swarming behavior. In one project, we perform experiments at the bacterial swarm front on agar, a soft substrate containing nutrients for the bacterial growth, to track the bacterial collective motion, with a focus on intercellular interactions that strongly affect the swarming behavior. In a second project, we incorporate mucin, the major component of mucus on airway and intestinal surfaces, in an agar gel, to study how the swarming motility of SM3 on the agar surface is dramatically enhanced. Our experiments show that mucin promotes swarming by abrogating contact line pinning, rendering the surface more slippery, and enabling the bacterial swarm to expand more readily and rapidly. The results of these studies show that the fundamental fluid mechanics and interfacial physics profoundly affect the swarming behavior. In a broader picture, the new knowledge of bacterial swarming motility might offer useful tips to biomedical and environmental applications.