FIG. 1.

Time-lapse observation of Z rings in E. coli, using FtsZ-GFP as a dilute label, expressed at about one-third the level of genomic FtsZ. The cells were induced to produce FtsZ-GFP for about 1 h and then immobilized on an agar pad for time-lapse observation at 37°C. (A) Three cells. We will ignore the two on the bottom (with a bright Z ring [left] and a dim Z ring [right]) and focus on the upper one (arrow), which is undergoing division. The constriction of the Z ring, its concurrent disassembly, and the assembly of new Z rings in the daughter cells are described in the text. (B) A cell with three Z rings (perhaps induced by excessive production of FtsZ-GFP). The upper Z ring (arrow) alternately opens into a short-pitch helix and collapses into an apparent circle. Frames from both panels A and B are taken from Movie S1 in the supplemental material.