The Z-Ring in Multicellular Cyanobacteria has a dynamic pearl necklace arrangement

Z-ring formation by FtsZ in the midcell is a key event in bacterial cell division. Results obtained with different super-resolution techniques have shown that the Z-ring is discontinuous, while live cell imaging has shown that FtsZ moves by treadmilling. In multicellular cyanobacteria, there have been no studies on the structure or dynamics of the Z-ring. In this study, we generated fully segregant mutants that express FtsZ fusions with fluorescent tags under the control of the native promoter in Anabaena sp., in which the Z-ring resembles a pearl necklace of dynamic arrangement with mobilization of FtsZ on the seconds scale. Division along filaments is asynchronous; however, manipulating the light conditions improves cell synchronization. Using correlative microscopy, we demonstrate that the DNA remains in the septum during constriction, therefore, the nucleoid occlusion mechanism does not apply here. To the best of our knowledge, this is the first live imaging of Z-ring behavior using fully segregated FtsZ mutants in a multicellular bacterial system.