FtsZ is an essential bacterial cell division protein, which orchestrates division by self-assembling into the Z ring. Despite its importance in division the mechanisms that allow assembly and subsequent constriction of the ring are not clear. The spatial resolution afforded by conventional wide-field fluorescence microscopy has not been sufficient to clearly visualize these processes in live cells. We have therefore utilized 3D-structured illumination microscopy (3D-SIM) and a new form of fast live 3D-SIM, known as OMX BlazeTM to generate 3D super resolution images of FtsZ and other divisome proteins in rod-shaped Bacillus subtilis cells and in spherical cells of Staphylococcus aureus.

Unlike conventional fluorescence microscopy, which depicts the Z ring as a continuous belt, 3D-SIM shows that FtsZ distribution within the ring is heterogeneous, with a bead-like arrangement in both organisms. Despite this similarity, the Z ring in S. aureus does not appear to assemble via remodeling of helical FtsZ structures like B. subtilis. Furthermore, we use ultra-fast 3D-SIM (OMX Blaze™) to uniquely show that the bead-like arrangement of FtsZ is dynamic throughout constriction. Our direct demonstration of FtsZ redistribution within the Z ring during constriction is consistent with the dynamic behavior of FtsZ proposed in the iterative pinching model (1, 2). Other core components of the divisome display a dynamic and heterogeneous localization pattern similar to FtsZ. Our data lead us to propose that FtsZ guides the divisome to adopt a similar localization pattern to ensure Z ring constriction only proceeds following the assembly of a mature divisome.