Interfacial morphodynamics of proliferating microbial communities

In nature, microbial communities with various cell types often coexist by occupying distinct spatial domains. Recent experiments on 2D growing multi-strain colonies have shown that cells become segregated into single-strain sectors. In some cases, the interface between these sectors becomes morphologically unstable, resulting in a rough, dented shape, while in other cases, the interface remains smooth. The factors that determine the shape of these interfaces—and how this affects cell interactions and overall community function—are still not well understood. Here, by combining theory, simulations, and experiments, we have established a biophysical description to describe the morphodynamics of interfaces between domains of two different cell types in a microbial community. Our model incorporates cell growth and cell-substrate friction, both of which can vary between single-strain sectors. We find that depending on the balance between different cell proliferation rates and substrate friction coefficients, the interface is either stable and smooth, or unstable, developing finger-like protrusions. We derive quantitative principles that predict when these different interfacial behaviors will occur, and our results align with both previous experimental findings and new experiments conducted in this study. Our work provides a biophysical basis for understanding the interfacial morphodynamics of proliferating microbial communities, as well as a broader range of proliferating active systems.