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Elife. 2019 Apr 30;8. pii: e42697. doi: 10.7554/eLife.42697.

A multiphase theory for spreading microbial swarms and films.

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John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, United States.
Kavli Institute for Bionano Science and Technology, Harvard University, Cambridge, United States.
Department of Physics, Harvard University, Cambridge, United States.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, United States.


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 we develop a generalized two-phase thin-film model that couples bacterial growth, extracellular matrix swelling, fluid flow, 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 of steady and unsteady expansion of microbial swarms and biofilms. Our results demonstrate how the physics of flow and transport in slender geometries serve to constrain biological organization in microbial communities.


B. subtilis; biofilms; biophysics; bioswarms; collective spreading; physics of living systems

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