Regulation of FtsZ levels inEscherichia coliin slow growth conditions

Abstract

1A key regulator of cell division in most walled bacteria is the FtsZ protein that assembles into 2 protofilaments attached to the membrane at midcell. These dynamic protofilament assemblies, known as 3 the Z-ring, act as a scaffold for more than two dozen proteins involved in synthesis of septal cell envelopes. 4What triggers the formation of the Z-ring during the cell cycle is poorly understood. In Escherichia coli 5 model organism, the common view is that FtsZ concentration is constant throughout its doubling time 6and therefore regulation of assembly should be controlled by some yet to be identified protein-protein 7 interactions. Here we show using quantitative analysis of newly developed fluorescent reporter that FtsZ 8 concentration varies in a cell-cycle dependent manner in slow growth conditions and that upregulation of 9FtsZ synthesis correlates with the formation of the Z-ring. About 4-fold upregulation of FtsZ synthesis in 10 the first half of the cell cycle is followed by its rapid degradation by ClpXP protease in the last 10% of the 11 cell cycle. The initiation of rapid degradation coincides with dissociation of FtsZ from the septum. 12Altogether, our data indicate that the Z-ring formation in slow growth conditions in E. coli is controlled by 13 a regulatory sequence where upregulation of an essential cell cycle factor is followed by its degradation. 14 Significance 16FtsZ is the key regulator for bacterial cell division. It initiates division by forming a dynamic ring-like 17 structure, the Z-ring, at the mid-cell. Here we show that, contrarily to the current paradigm, FtsZ 18 concentration in Escherichia coli model organism varies throughout cell cycle in slow growth conditions. 19Faster FtsZ synthesis in the first half of the cell cycle is followed by its rapid degradation by ClpXP protease 20 in the end of the cell cycle. Upregulation of FtsZ synthesis correlates with the formation of the Z-ring. Our 21 data demonstrates that in slow growth E. coli cell division progresses according to paradigm where 22 upregulation of essential cell cycle factor is followed by its degradation. 23