Collective bacterial swarming on rough surfaces

Bacteria live and grow in spatially structured complex environments, e.g., the human gut, where they regulate key intestinal responses to inflammation. While motile bacteria can display collective behaviors such as swarming in these environments, how physical features of inflammation, such as increased tissue roughness, affects bacterial swarming is poorly understood. Motivated by recent experiments that suggest swarming is enhanced on inflamed tissues, we model the bacterial swarm as a thin layer of an active fluid on a rough surface. A lubrication approximation yields both a passive and active contribution from roughness that can compete to generate complex flow patterns. By using numerical simulations, we quantify the role of surface patterns in controlling swarming flows and identify regimes of flow enhancement that we compare with experimental data.