Overcoming physical obstacles: a collective microbial solution to a shared problem*

Bacterial biofilms are the most pervasive life form on the planet having adapted to a wide range of living conditions. While invading new territory in the wild, biofilms periodically encounter physical barriers, including populations of other bacteria that can be so densely packed to completely halt the forward motion of individual cells. How do biofilms overcome such a challenge?

 

Using time-lapse microscopy on expanding biofilms of B. subtilis crashing against populations of E. coli of variable density and width, we find that the biofilm population exhibits different collective strategies to bypass the barrier on its path, often requiring coordination of cell behaviour across thousands of cells. In particular, while rafts of swarming cells are sufficient to break through thin barriers, large barriers trigger a “vascularization” process during which some cells switch from motile to matrix producers to create protected channels that slowly penetrate the barrier. The two strategies consistently follow a precise chronological order, suggesting that the biofilm behaviour is a response to the increasing mechanical stress generated in the attempt of breaking through the barrier. To test this hypothesis, we perform molecular dynamics simulations of populations of particles that can switch from active to sticky as a function of their local mechanical stress and identify the minimal ingredients necessary to recapitulate the experimental results.

 

This work is in collaboration with Dr. Luis Ruiz Pestana, University of Miami.