Elasticity and wrinkled morphology of Bacillus subtilis pellicles |
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Authors: | Miguel Trejo Carine Douarche Virginie Bailleux Christophe Poulard Sandrine Mariot Christophe Regeard Eric Raspaud |
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Institution: | aLaboratoire de Physique des Solides, Université Paris-Sud, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8502, F-91405 Orsay, France; and;bInstitut de Génétique et Microbiologie, Université Paris-Sud, Centre National de la Recherche Scientifique, Unité Mixte de Recherche 8621, F-91405 Orsay, France |
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Abstract: | Wrinkled morphology is a distinctive phenotype observed in mature biofilms produced by a great number of bacteria. Here we study the formation of macroscopic structures (wrinkles and folds) observed during the maturation of Bacillus subtilis pellicles in relation to their mechanical response. We show how the mechanical buckling instability can explain their formation. By performing simple tests, we highlight the role of confining geometry and growth in determining the symmetry of wrinkles. We also experimentally demonstrate that the pellicles are soft elastic materials for small deformations induced by a tensile device. The wrinkled structures are then described by using the equations of elastic plates, which include the growth process as a simple parameter representing biomass production. This growth controls buckling instability, which triggers the formation of wrinkles. We also describe how the structure of ripples is modified when capillary effects are dominant. Finally, the experiments performed on a mutant strain indicate that the presence of an extracellular matrix is required to maintain a connective and elastic pellicle. |
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Keywords: | biofilm elasticity biofilm growth wrinkles formation |
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