3D-SIM Super Resolution Microscopy Reveals a Bead-Like Arrangement for FtsZ and the Division Machinery: Implications for Triggering Cytokinesis

Ftsz is a tubulin-like gtpase that is the major cytoskeletal protein in bacterial cell division. it polymerizes into a ring,called the z ring,at the division site and acts as a scaffold to recruit other division proteins to this site as well as providing a contractile force for cytokinesis. to understand how ftsz performs these functions,the in vivo architecture of the z ring needs to be established,as well as how this structure constricts to enable cytokinesis. conventional wide-field fluorescence microscopy depicts the z ring as a continuous structure of uniform density. here we use a form of super resolution microscopy,known as 3d-structured illumination microscopy (3d-sim),to examine the architecture of the z ring in cells of two gram-positive organisms that have different cell shapes: the rod-shaped bacillus subtilis and the coccoid staphylococcus aureus. we show that in both organisms the z ring is composed of a heterogeneous distribution of ftsz. in addition,gaps of fluorescence were evident,which suggest that it is a discontinuous structure. time-lapse studies using an advanced form of fast live 3d-sim (blaze) support a model of ftsz localization within the z ring that is dynamic and remains distributed in a heterogeneous manner. however,ftsz dynamics alone do not trigger the constriction of the z ring to allow cytokinesis. lastly,we visualize other components of the divisome and show that they also adopt a bead-like localization pattern at the future division site. 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. © 2012 strauss et al.