3D Motility Measurements of <i>Myxococcus xanthus </i>Fruiting Body Formation

Myxococcus xanthus is a rod-shaped, soil-dwelling bacterium with striking manifestations of collective behavior. When starved, cells aggregate to form 3D mound-like structures known as fruiting bodies containing hundreds of thousands of cells. The aggregation process has been previously analyzed with motility-induced phase separation (MIPS). M. xanthus induce this phase separation by tuning their speed and frequency of cell reversal. In this 2D model, cells cluster through a jamming process similar to reversing active Brownian particles, but in 3D, cells extrude from the surface and migrate into a motile layered structure, a process better described by dewetting. We present here cell motility measurements in 3D during fruiting body formation for a dewetting model. We track sparsely labelled M. xanthus in 3D using confocal microscopy during fruiting body formation (24-48h). We extract cell speed and reversal frequencies, two key motility parameters of the MIPS model, and analyze their dependencies on time after starvation to better understand the mechanism behind aggregation. Cell tracks from different regions of fruiting bodies also provide information on how cells move and organize within these structures.