FTSZ-SPIRALS AND FTSZ-ARCS DETERMINE THE SHAPE OF THE INVAGINATING SEPTA IN SOME MUTANTS OF ESCHERICHIA-COLI

The essential cell division protein FtsZ forms a dynamic ring structur e at the future division site. This Z-ring contracts during cell divis ion while maintaining a position at the leading edge of the invaginati ng septum. Using immunofluorescence microscopy we have characterized t wo situations in which non-ring FtsZ structures are formed. In ftsZ26 (temperature sensitive, Ts) mutant cells, FtsZ-spirals are formed and lead to formation of spirally invaginating septa, which in turn cause morphological abnormalities. In rodA(sui) mutant cells, which grow as spheres instead of rods, FtsZ-arcs are formed where asymmetric septal invaginations are initiated. The FtsZ-arcs later mature into complete FtsZ-rings. Our data show that Z-spirals and Z-arcs can contract and t hat in doing so, they determine the shape of the invaginating septa. T hese results also strongly suggest that in normal cell division, FtsZ is positioned to a single nucleation site on the inner membrane, from which it polymerizes bidirectionally around the cell circumference to form the Z-ring.