  Anisotropic collective patterns occur frequently in the morphogenesis of 2D
biofilms. These patterns are often attributed to growth regulation mechanisms
and differentiation based on gradients of diffusing nutrients and signalling
molecules. Here, we employ a model of bacterial growth dynamics to show that
even in the absence of growth regulation or differentiation, confinement by an
enclosing medium such as agar can itself lead to stable pattern formation over
time scales that are employed in experiments. The underlying mechanism relies
on path formation through physical deformation of the enclosing environment.
