What shapes bacterial biofilms? A Physics perspective.

Biofilms are aggregates of microorganisms in which cells are embedded in a self-secreted matrix of extracellular polymeric substances (EPS) and are adherent to each other and/or to a surface. The composition of the matrix can vary greatly depending on the microorganisms present and the environmental conditions. However, its functions are universal: the matrix forms the scaffold of the biofilm structure, is responsible for adhesion and cohesion, keeps the cells close, thus favoring interactions, and protects the microbial community from chemical and mechanical insults. Despite its importance, the matrix remains the least understood component of biofilms.

Our work aims to understand how the material properties of the biofilm matrix determine biofilm morphology and mechanical properties. We present examples of biofilms grown in different environmental conditions, ranging from the air-solid interface of agar plates to surfaces exposed to fluid flow and porous media, and by different bacterial species. In each case, we show that the interplay between biology-driven forces, i.e., growth, and physics-driven ones, i.e., surface adhesion, osmotic pressure, and shear stress, controls biofilm morphology, rheology, and, ultimately, affects the physiological protective function of biofilms. By shedding light on this interplay, we can control biofilm development, showing the prominent role physics can play in developing novel antimicrobial and antifouling strategies.