  In growing active matter systems, a large collection of engineered or living
autonomous units metabolize free energy and create order at different length
scales as they proliferate and migrate collectively. One such example is
bacterial biofilms, which are surface-attached aggregates of bacterial cells
embedded in an extracellular matrix. However, how bacterial growth coordinates
with cell-surface interactions to create distinctive, long-range order in
biofilms remains elusive. Here we report a collective cell reorientation
cascade in growing Vibrio cholerae biofilms, leading to a differentially
ordered, spatiotemporally coupled core-rim structure reminiscent of a blooming
aster. Cell verticalization in the core generates differential growth that
drives radial alignment of the cells in the rim, while the radially aligned rim
in turn generates compressive stresses that expand the verticalized core. Such
self-patterning disappears in adhesion-less mutants but can be restored through
opto-manipulation of growth. Agent-based simulations and two-phase active
nematic modeling reveal the strong interdependence of the driving forces for
the differential ordering. Our findings provide insight into the collective
cell patterning in bacterial communities and engineering of phenotypes and
functions of living active matter.
