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Zusammenfassung:
Bacterial biofilms represent a major form of microbial life on Earth and
serve as a model active nematic system, in which activity results from
growth of the rod-shaped bacterial cells. In their natural environments,
ranging from human organs to industrial pipelines, biofilms have evolved
to grow robustly under significant fluid shear. Despite intense
practical and theoretical interest, it is unclear how strong fluid flow
alters the local and global architectures of biofilms. Here, we combine
highly time-resolved single-cell live imaging with 3D multiscale
modeling to investigate the mechanisms by which flow affects the
dynamics of all individual cells in growing biofilms. Our experiments
and cell-based simulations reveal three quantitatively different growth
phases in strong external flow and the transitions between them. In the
initial stages of biofilm development, flow induces a downstream
gradient in cell orientation, causing asymmetrical dropletlike biofilm
shapes. In the later developmental stages, when the majority of cells
are sheltered from the flow by the surrounding extracellular matrix,
buckling-induced cell verticalization in the biofilm core restores
radially symmetric biofilm growth, in agreement with predictions of a 3D
continuum model.
