Outer Membrane Structures Regulate Proteus Mirabilis Swarm Motility

Abstract

The Gram negative bacterium Proteus mirabilis engages in a social, surface-based motility called swarming. Swarming requires two broad phenomena: swarmer cell development and population migration. The genetic requirements for initiation of swarmer cell development have been well characterized; however, the differential requirements for swarmer cell development and swarmer cell motility remain poorly understood. Here we characterize the roles of two sugar-based outer membrane structures in regulating P. mirabilis swarming. First, we demonstrate that cells require the poorly understood Enterobacterial Common Antigen (ECA) for maintenance of cell envelope integrity during swarmer cell development; this functions occurs in part through a cell envelope stress-sensing pathways. Next, we demonstrate that cells require lipopolysaccharide O-antigen for population expansion. We demonstrate that agar concentration (a proxy for surface wettability) modulates the behavior of swarming cells at the micron and centimeter scale, and propose that O-antigen enhances swarming through enhanced wettability of the local surface environment. Altogether, this research demonstrates that two seemingly similar sugar-based molecules (ECA and O-antigen) play different roles at different scales in promoting P. mirabilis swarm motility. These molecules are virulence-associated and shared across many species of bacteria, including known pathogens. As such, this work may have broad implications for bacterial behavior and virulence.