Shape up to run - how bacterial motilities impact selective cellular morphologies

School of Natural Sciences, University of California, Merced

Bacteria come in consistent shapes and sizes, which serve as one way for an individual to interact with the environment. Despite the fact that a specific morphology is important within a species, there is a lack of direct evidence on how cellular morphology affects bacterial fitness, especially regarding their dispersal capabilities and virulence factors. In this talk, I will discuss how fluid-structure interactions can potentially play a role in the evolution of cellular morphology, using both theoretical and experimental approaches. First, I will show a coupled effect of the cell shape and the flagellar alignment on the motility of rod-shaped bacteria. I will demonstrate that such an effect is sensitive to the volume of the cell body through a hydrodynamic model: when the volume is sufficiently large, the bacterium prefers a cell body in blunt shapes and oriented toward the swimming direction for optimal swimming speed; when the volume is below a critical value, determined by the flagellar geometry, the bacterium prefers an elongated shape that points away from the direction of swimming and thus wobbles. I will also compare this result with our experimental observations on several different species to show whether bacteria have "learned" fluid mechanics to shape their bodies. Finally, I will discuss the impact of motilities in the context of multi-cellular life forms, in which the morphology can be dynamically modified by addition or removal of individual bacteria. I will show that new forms of motilities can emerge from this multi-cellular morphology and its interaction with the specific mechanical environments, such as a solid-liquid interface.