Spatial Genetic Structure in Growing Bacterial Monolayers on Curved Surfaces

Bacterial communities are ubiquitous in nature, including as monolayers colonizing the complex surfaces of animal digestive systems, and play an important role in maintaining genetic diversity in microbiomes. During surface colonization, populations experience a reduction in genetic diversity by a de-mixing of the population into monoclonal regions. Growing monolayer colonies can partially counteract this diversity loss through emergent short range nematic order that results from mechanical interactions between rod-like cells, as has been previously demonstrated on flat, uniform surfaces. Recent work has revealed that surfaces of constant curvature can reduce nematic order length scales through curvature-induced buckling. This opens the question of how surface curvature interacts with active nematic dynamics and population genetics. Here, we use Brownian dynamics simulations of growing and dividing hard-rods on surfaces of non-uniform curvature to show that surfaces of high curvature can suppress active nematic effects and thus enhance genetic de-mixing. Additionally, we find evidence that singularities in the nematic order, called topological defects, that are produced in such monolayers correlate with Gaussian curvature, as has been observed in liquid crystal systems.