The dynamics of sibling rivalry across spatially extended networks of bacterial colonies

Bacteria often form biofilms with complex spatiotemporal structures. Much work has provided insights into biofilm formation by investigating the dynamics within a single colony, but numerous experiments have unexpectedly revealed antagonistic interactions that inhibit expansion of neighboring colonies, even when they consist of sibling cells of the same strain. Studying sibling rivalry with the organism E. faecalis, an opportunistic pathogen, we observe an intriguing behavior: spatially separated, but otherwise identical, colonies merge into a single larger colony only when initially separated by a sufficiently small distance; at larger separations, founder colonies remain separated by a cell-free zone due to growth inhibition. Such inter-colony inhibition has been observed both within and across species, yet the dynamics and functional consequences of this general mechanism are not fully understood. What determines the critical distance within which colonies must originate to merge into a cohesive unit? How does this scale dynamically change as cells proliferate? To address such questions, we developed high-throughput experiments of spatially extended colony networks created on agar plates with an open-source pipetting robot. Here, we investigate how the initial spatial distribution of cells, rates of intrinsic growth and diffusion, and environmental stress determine the strength and scale of intra- and inter-colony inhibition.