Mechanoregulation of biofilm homeostasis

Microbial communities are commonly found as biofilms: contiguous groups of cells held together by a self-secreted extracellular matrix of polymeric substances. To maintain the cohesion of the biofilm or to enable dispersal, cells must regulate matrix production. During growth, single biofilm-dwelling cells generate a mechanical stress onto the viscoelastic matrix. These forces influence biofilm architecture and morphogenesis. However, how they regulate the physiology of the cell population in the biofilm is unknown. To explore the relationship between constrained growth and bacterial decision-making, we investigated the physiology of bacteria confined in synthetic hydrogel matrices. We embed P. aeruginosa, a model organism for biofilm studies and an opportunistic pathogen, in PEG-hydrogels. By tuning the mechanical properties of the hydrogel, we found that the size of embedded biofilms decreases with the stiffness of the surrounding hydrogel. We show that measurements of the transcriptional profiles of embedded cells allow us to identify potential mechanosensors regulating biofilm integrity. Finally, using reporter fusions to monitor the transcriptional response of single PEG-embedded cells, we demonstrate that cells respond to constrained growth. Altogether, our study will highlight the role of mechanics in guiding cellular decisions within a biofilm.