Laboratoire Matière et Systèmes Complexes

Bacterial biofilms are communities of bacteria associated with biological or artificial surfaces. They form by a nucleation - growth mechanism coupled with the production of polysaccharide-rich extracellular matrix likely to both protect and stabilize the edifice. These widespread structures have a strong socio-economic impact both deleterious ? like in nosocomial diseases ? or beneficial ? in many biotechnological applications. The complex 3D-architecture is viewed as a highly heterogeneous material but very little is known about its internal dynamics. In order to better control these biological organisations, a better understanding of their inside features is required. To gain insight into biofilm core properties, we have designed an experiment dedicated to measuring local physical parameters of this living material. The principle of the experiment consists in achieving stealth infiltration of the material with micrometric magnetic particles enabling local remote stress loading. In this presentation, I will describe the main steps of the run and show the first results obtained on E. coli biofilms. I will pay special attention to the effect of biofilm growth shear stress on the values of the material visco-elastic parameters and on their spatial distribution. As well, I will consider the possible dependence of the biofilm physical properties on individual cell molecular properties. Eventually, I will conclude by giving the 3D physical picture of a bacterial biofilm emerging from these findings.