  We investigate the emergence of global alignment in colonies of dividing
rod-shaped cells under confinement. Using molecular dynamics simulations and
continuous modeling, we demonstrate that geometrical anisotropies in the
confining environment give rise to imbalance in the normal stresses, which, in
turn, drives a collective rearrangement of the cells. This behavior crucially
relies on the colony's solid-like mechanical response at short time scales and
can be recovered within the framework of active hydrodynamics upon modeling
bacterial colonies as growing viscoelastic gels characterized by Maxwell-like
stress relaxation.
