Isotropic Imaging of Three-dimensional Nematic Order in Myxococcus xanthus Colonies*

The soil bacterium Myxococcus xanthus (M. xanthus) exhibits unique collective motility behaviors characterized in part by long range nematic ordering of cells. Under favorable conditions, early M. xanthus colonies are largely flat, composed of only one to a few layers of cells which coordinate their movement to swarm or stream over a solid surface. Recent work has shown that M. xanthus layer formation is associated with topological defects in the nematic alignment of moving cells which results in high pressure nodes that extrude bacteria upwards. Due to limitations in the axial resolution of confocal microscopy, it is as yet unclear whether the nematic alignment of cells is continuous across successive layers. Additionally, when starved, M. xanthus aggregates to form much more 3-dimensional mounds, called fruiting bodies, inside which many cells sporulate to endure the harsh conditions. The organization of cells within fruiting bodies, and whether the population acts as a 3D active nematic, are not known. To resolve details of cell position and orientation, I use a dual-view inverted selective plane illumination microscope (diSPIM) capable of isotropic 3D resolution. My project investigates cell layering and alignment to ask if fruiting bodies are composed of discrete layers of nematically ordered cells.