Effects of cell density on swarming SM3 bacteria

Swarming behavior is a common trait observed in many species of flagellated bacteria. It occurs when a growing population of cells expands on an agar surface, resulting in collective motion. We investigate the swarming behavior of Enterobacter sp. SM3, a gut bacterium that has recently been identified to provide a physiological benefit to lab mice suffering intestinal inflammation. We found that the collective dynamics of SM3 are highly sensitive to cell density. This sensitivity underscores how the interaction between individual cells are a key determinant of these dynamic patterns of motion in bacterial swarms. Thus, accurate measurements of cell density, cell positions and orientations, as well as observing flagella within the swarm are all essential to understand the mechanisms governing the observed collective behavior.