  Like other developmental systems, bacteria in biofilms reproducibly
self-organize into ordered patterns during development. Despite recent progress
in single-cell imaging, the physical principles underlying the long-range
ordering in biofilm remain unknown. Using Vibrio cholerae as a model biofilm
former, we uncover the mechanical blueprint that governs biofilm
self-patterning. We show that, through mechanical instabilities at the
single-cell level, a biofilm spontaneously creates spatially segregated zones
of anisotropic growth, which drive macroscopic ordering. We develop a two-phase
active nematic model to quantitatively predict the biofilm developmental
process and to provide guidance for strategies to pattern biofilms. We verify
our theory by mutagenesis and by optically manipulating cell growth. Our
conclusions are potentially generalizable to a wide variety of developmental
systems with growth-induced flows.
