Minding the gap: collective determinants of multiscale structure across interacting bacterial colonies

Abstract

A bacterial colony rarely exists in isolation - in natural habitats, colonies interact to form spatially structured communities across length and time scales. Eco-evolutionary feedbacks link these scales, such that structures at one level can influence another. A commonly observed multi-colony trait is the formation of a stable gap between growing colonies (even when isogenic) but, despite its ubiquity, the underlying mechanisms are poorly understood. To address this, we develop a high-throughput robotic platform to track population dynamics across spatially extended networks of colonies. We show that isogenic colonies of the opportunistic pathogen Enterococcus faecalis spontaneously form stable gaps when inoculated beyond a critical distance apart. By combining quantitative modeling and experiments, we show that both nutrient competition and direct growth inhibition control colony morphology and expansion of interacting colonies. We identify distinct regimes of gap formation, relating intra- and inter-colony spatial patterns to ecological interactions mediated at the cellular scale. Together, our results suggest that antagonism, even between isogenic populations through self-inhibition, is likely a common behavior of bacterial species in general.