Dynamics of spreading microbial swarms and films

Abstract

Bacterial swarming and biofilm formation are collective multicellular phenomena through which diverse microbial species colonize and spread over water-permeable tissue. During both modes of surface translocation, fluid uptake and transport play a key role in shaping the overall morphology and spreading dynamics. Here, using Bacillus subtilis as our model experimental system, we develop a generalized two-phase thin-film model that couples hydrodynamics, mechanics, osmotic flux and nutrient transport to describe the expansion of both highly motile bacterial swarms, and sessile bacterial biofilms. We show that swarm expansion corresponds to steady-state solutions in a nutrient-rich, capillarity dominated regime. In contrast, biofilm colony growth is described by transient solutions associated with a nutrient-limited, extracellular polymer stress driven limit. We apply our unified framework to explain a range of recent experimental observations associated with the shape, form and dynamics of Escherichia coli and Bacillus subtilis swarms and biofilms. Our results demonstrate how hydrodynamics and transport serve as key physical constraints in regulating biological organization and function in microbial communities.