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Séminaire de Julien Dervaux

On growth and form of Bacillus Subtilis biofilms


Julien Dervaux

Rockfeller University, New York.

On growth and form of Bacillus Subtilis biofilms

A general feature of mature biofilms is their highly heterogeneous architecture that partitions the microbial city into sectors with specific micro-environments. To understand how this heterogeneity arises, I have investigated the sequence of events leading from a single cell to a fully developed microbial community of the model organism Bacillus subtilis. To trigger biofilm assembly, I show that an initially single cell must produce a cellular cluster of ? 650 μm2, irrespectively of the environmental parameters (substrate stiffness and nutrient concentration). Once present, matrix producing cells tend to stay connected with their lineage after division and long bacterial chains form. This morphological transition gives rise to a mechanism of front propagation that qualitatively differs from that of short, undifferentiated cells. In addition to the process of cellular chaining, the biomass stickiness also strongly hinders the reorganization of cells within the biofilm. As a consequence, local height fluctuations of the growing bacterial layer coarsen in time and ultimately lead to the formation of a rough biofilm surface exhibiting self similar properties. A biophysical model associating the nonlocality and the stochasticity of the growth process reproduces the experimental features.