Viewing biofilm formation through a multifocal lens of physics and biology

Recent studies on the formation, organisation and dynamics of biofilms highlight the interplay between physical forces and biological programs. Two complementary generalised pathways that explain the mechanisms driving biofilm formation have emerged. In the first pathway, where physical forces precede the biological program, the initial expansion of cells leads to cell clustering or aggregation prior to the production of extracellular polymeric substances (EPS). The second pathway describes an initial biologically prompted production of EPS, which introduces new biophysical interactions within the EPS, such as by phase separation, macromolecular crowding, excluded volume interactions and intermolecular cross-linking. In practice, which of the two pathways is adopted is ultimately determined by the specificities of the biofilm and the local microenvironment, each leading to the formation of robust, viscoelastic biofilm. Within this framework, we further highlight here recent findings on the role of higher-order structures in matrix gelation and phase separation of EPS in promoting the clustering of bacteria. We assert that examining biofilms through the combined lens of physics and biology promises new and significant methodological and conceptual advancements in our understanding of biofilms.