  Order and alignment are ubiquitous in growing colonies of rod-shaped bacteria
due to the nematic properties of the constituent particles. These effects are
the result of the active stresses generated by growth, passive mechanical
interactions between cells, and flow-induced effects due to the shape of the
confining container. However, how these contributing factors interact to give
rise to the observed global alignment patterns remains elusive. Here, we study,
in-silico, colonies of growing rod-shaped particles of different aspect ratios
confined in channel-like geometries. A spatially resolved analysis of the
stress tensor reveals a strong relationship between near-perfect alignment and
an inversion of stress anisotropy for particles with large length-to-width
ratios. We show that, in quantitative agreement with an asymptotic theory,
strong alignment can lead to a decoupling of active and passive stresses
parallel and perpendicular to the direction of growth, respectively. We
demonstrate the robustness of these effects in a geometry that provides less
restrictive confinement and introduces natural perturbations in alignment. Our
results illustrate the complexity arising from the inherent coupling between
nematic order and active stresses in growing active matter which is modulated
by geometric and configurational constraints due to confinement.
