FtsZ ring formation without subsequent cell division after replication runout in Escherichia coli

In this report, we have investigated cell division after inhibition of init iation of chromosome replication in Escherichia coli. In a culture grown to the stationary phase, cells containing more than one chromosome were able to divide some time after restart of growth, under conditions not allowing initiation of chromosome replication. This shows that there is no requireme nt for cell division to take place within a certain time after initiation o f chromosome replication. Continued growth without initiation of replicatio n resulted in filamented cells that generally did not have any constriction s. Interestingly, FtsZ rings were formed in a majority of these cells as th ey reached a certain cell length. These rings appeared and were maintained for some time at the cell quarter positions on both sides of the centrally localized nucleoid. These results confirm previous findings that cell divis ion sites are formed independently of chromosome replication and indicate t hat FtsZ ring assembly is dependent on cell size rather than on the capacit y of the cell to divide. Disruption of the mukB gene caused a significant i ncrease in the region occupied by DNA after the replication runout, consist ent with a role of MukB in chromosome condensation. The aberrant nucleoid s tructure was accompanied by a shift in FtsZ ring positioning, indicating an effect of the nucleoid on the positioning of the FtsZ ring. A narrow cell length interval was found, under and over which primarily central and non-c entral FtsZ rings, respectively, were observed. This finding correlates wel l with the previously observed oscillatory movement of MinC and MinD in sho rt and long cells.