The mechanisms of spatial pattern transition in motile bacterial collectives

To understand how individual behaviors contribute to collective actions across scales---ranging from molecular interactions to animal populations---it is essential to identify the fundamental rules that govern these interactions. Myxococcus xanthus , a bacterial predator, can produce very large multicellular patterns, transitioning from a swarming behavior to a rippling behavior due to changes in the local environment within and around prey colonies. Through a combination of high-resolution microscopy and theoretical analysis, we demonstrate that this transition can be explained by two simple properties, local cellular alignment guided by an extracellular matrix and the ability of cells to resolve congestion by reversing. Furthermore, we show that a tunable refractory period in the reversal control system enables a wide range of collective adaptations, allowing cells to synchronize during rippling and relieve congestion during swarming. Remarkably, our models suggest that these transitions can occur without genetic regulation changes, and result in stable spatial domains that facilitate local differentiation.