Self-generated trail networks promote aggregation in multicellular bacteria <i>Myxococcus xanthus</i>

Abstract Organismal development is strongly influenced by the environment, which organisms can, in turn, actively modify. However, how such self-driven environmental changes shape multicellular development remains poorly understood. Myxococcus xanthus is a model bacterium for studying the transition to aggregative multicellularity, as it can develop multicellular fruiting bodies. During this process, M. xanthus cells modify their substrate by forming trails that bias the movement of other cells. How these substrate modifications change over developmental time and whether they scale up to influence aggregation at the population level remain unknown. Here, we tracked a population of M. xanthus over the first 48 h of development, quantifying trail extension, trail network formation and connectivity and the size of cellular aggregates. Trail length, area and connectivity increased over time and exhibited an abrupt transition into a highly connected network, consistent with a percolation process that facilitates cellular encounters. This transition was accompanied by the emergence of progressively larger cellular aggregates. Together with other lines of evidence, these results indicate that this cell-driven environmental modification promotes multicellular aggregation. Our findings provide new insights and ways to study how microorganisms can actively shape key aspects of their own multicellular development through environmental modification.