Heritable adhesion geometries and mechanosensing of surfaces by biofilm-forming bacteria

Biofilms are dense, interacting communities of single-celled organisms that are bound to each other with a self-produced polymer matrix.~ Biofilms have devastating clinical impact as they increase resistance to antibiotics and the immune system as well as the production of virulence factors that damage the host.~ Here we examine effects very early in biofilm development, when the infection is still in a stage of a few cells not yet characterized by high biofilm densities. ~\textit{Pseudomonas aeruginosa}, an opportunistic human pathogen, produces multiple extracellular polysaccharides that form the biofilm's structuring matrix.~ We have recently shown that the two primary polysaccharides, Pel and Psl, have distinct roles in controlling the mechanics of single-cell adhesion to a surface -- Psl dominates adhesion to the surface, and Pel makes the bacterium lie down flat (Cooley \textit{et al}., 2013 Soft Matter). Here, we show that expressing Pel alters the symmetry of Psl's distribution on the surface of rod-shaped \textit{Pseudomonas}. We also show that expressing Pel decreases the work of detachment from the surface. It seems paradoxical that a biofilm-forming organism should pay the cost of maintaining and making a gene product that reduces the energy input required to detach it from a surface. Therefore, we probe the possibility that a flat-lying bacteria may better sense a solid surface and change its signaling state accordingly.