Mechanical stress fluctuations in Myxococcus xanthus monolayers revealed by traction force microscopy

During development, a population of Myxococcus xanthus cells transitions from a two-dimensional monolayer to three-dimensional fruiting bodies. The initial motion of cells into the third dimension occurs at special points in the monolayer where there is a topological defect in the cellular alignment field. To understand how these defects are related to three-dimensional motion, we need to observe both how cells move and the relevant mechanical forces. Using traction force microscopy, we map out the spatial distribution of forces exerted by M. xanthus cells on a soft hydrogel substrate and link the position of defects to the distribution of stresses. We reveal strong stress fluctuations within the system, which ultimately drive the initial stage of fruiting body development.