Capillary attraction facilitates bacterial collective dynamics: Experiment

When placed on an agar gel, small groups of the soil-dwelling bacteria M. xanthus move, merge with other groups, and eventually coarsen into a single monolayer. Here, we use surface profilometry to quantify the water meniscus that wets surface-attached cells, and show that the capillary attraction mediated by these menisci shapes the structure and dynamics of M. xanthus group motility. We construct a device that allows us to systematically vary the meniscus length of wetted cells and use time-lapse microscopy to quantify how changes in cell-cell capillary attraction effect both the mobility, shape, and lifetime of cell groups. We further show how such changes in the behavior of small groups manifest themselves in the eventual coarsening behavior of the population. Together with a computational model, our results, establish a basic mechanism for how environmental fluctuations in soil hydration may affect the collective behaviors of natural populations of M. xanthus.