Bacteria sense and respond to the mechanics of the surface to which they attach*

The attachment of bacteria to a surface is often a key initial step in the development of biofilms, communities of bacteria that are significant contributors to disease, fouling, and damage to the built environment. Understanding how bacteria sense surface attachment and, in response, begin the process of biofilm initiation, should give rise to new avenues to biofilm prevention as well as advance basic science. Here, we examine the relationship between substrate stiffness, mechanical deformation of the bacterial cell, accumulation of bacteria on the surface, and dynamics of an intracellular signal that control biofilms development. Pseudomonas aeruginosa, a widely-used model organism for biofilm development and a common hospital-acquired pathogen. We find that when the chemistry of a gel substrate is held constant but the effective elasticity is increased, more bacteria accumulate and signaling activates earlier. The response to the substrate mechanics at times greater than one hour after attachment depends on different cellular structures than at earlier times. Thus, the bacterial mechanosensing leading to biofilm development is likely a multi-step process involving more than one sensory element.