(566e) Mechanical Principles of Biofilm Formation Revealed By Single-Cell Resolution Imaging of V. cholerae Biofilms

Biofilms are surface-associated bacterial communities embedded in an extracellular matrix. Biofilm cells are more resistant to antibiotics than their planktonic counterparts, which is a major problem in the context of chronic infections. Investigations so far have focused on the genetic and regulatory features driving biofilm formation. However, still lacking is a fundamental biophysical understanding of how bacteria, in time and space, build these three-dimensional structures that attach to surfaces and resist mechanical and chemical perturbations. During this talk, I will present a new methodology to image living, growing bacterial biofilms from single founder cells to ten thousand cells at single-cell resolution. Using the human pathogen Vibrio cholerae as a model biofilm former, we discovered the key mechanical forces underpinning the architectural evolution of the biofilm. By combining mutagenesis, matrix labeling, and computer simulations, we demonstrated that surface-adhesion-mediated compression, coupled with the directional proliferation of the rod-shaped cells, causes V. cholerae biofilms to transition from a two-dimensional branched morphology to a dense, ordered three-dimensional cluster.

In the second half of the talk, I will explore the consequences to biofilm growth and robustness when the biofilm matrix functions as a material that is responsive to environmental perturbations such as changes in osmotic pressure. Again using Vibrio cholerae as the model organism, we showed that matrix production enables biofilm-dwelling bacterial cells to establish an osmotic pressure differential between the biofilm and the external environment. The pressure difference promotes colony biofilm expansion on nutritious surfaces, controls growth of submerged biofilms, and enables matrix-producing cells in biofilms to exclude non-matrix-producing cheaters and to resist invasion by planktonic cells. This finding have broad implications for other biofilm-forming bacterial species, as principles underlying osmotic pressure responses of these gel-like materials should be universal.