title: Bacillus subtilis Bacteria Generate an Internal Mechanical Force within a Biofilm.
abstract: A key issue in understanding why biofilms are the most prevalent mode of bacterial life is the origin of the degree of resistance and protection that bacteria gain from self-organizing into biofilm communities. Our experiments suggest that their mechanical properties are a key factor. Experiments on pellicles, or floating biofilms, of Bacillus subtilis showed that while they are multiplying and secreting extracellular substances, bacteria create an internal force (associated with a -80±25 Pa stress) within the biofilms, similar to the forces that self-equilibrate and strengthen plants, organs, and some engineered buildings. Here, we found that this force, or stress, is associated with growth-induced pressure. Our observations indicate that due to such forces, biofilms spread after any cut or ablation by up to 15-20% of their initial size. The force relaxes over very short timescales (tens of milliseconds). We conclude that this force helps bacteria to shape the biofilm, improve its mechanical resistance, and facilitate its invasion and self-repair.
authors.affiliation: Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay Cedex, France.
authors.forename: Carine
authors.initials: C
authors.lastname: Douarche
authors.affiliation: Laboratoire de Mécanique des Solides, CNRS-UMR 7649, École Polytechnique, Palaiseau, France.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Allain
authors.affiliation: Laboratoire de Physique des Solides, Université Paris-Sud, CNRS-UMR 8502, Orsay Cedex, France. Electronic address: eric.raspaud@u-psud.fr.
authors.forename: Eric
authors.initials: E
authors.lastname: Raspaud
mesh_terms: D001412:Bacillus subtilis / Q000502:physiology*; D018441:Biofilms; D011312:Pressure; D013314:Stress, Mechanical