FtsZ is the key regulator of bacterial cell division. It initiates division by forming a dynamic ring-like structure, the Z-ring, at the mid-cell. What triggers the formation of the Z-ring during the cell cycle is poorly understood. In Escherichia coli, the common view is that FtsZ concentration is constant throughout its doubling time and therefore regulation of assembly is controlled by some yet-to-be-identified protein-protein interactions. Using a newly developed functional, fluorescent FtsZ reporter, we performed a quantitative analysis of the FtsZ concentration throughout the cell cycle under slow growth conditions. In contrast to the common expectation, we show that FtsZ concentrations vary in a cell cycle-dependent manner, and that upregulation of FtsZ synthesis correlates with the formation of the Z-ring. The first half of the cell cycle shows an approximately fourfold upregulation of FtsZ synthesis, followed by its rapid degradation by ClpXP protease in the last 10% of the cell cycle. The initiation of rapid degradation coincides with the dissociation of FtsZ from the septum. Altogether, our data suggest that the Z-ring formation in slow growth conditions in E. coli is partially controlled by a regulatory sequence wherein upregulation of an essential cell cycle factor is followed by its degradation.
Highlights d Z-ring formation in E. coli is preceded by formation of transient FtsZ assemblies d The assemblies show rapid growth and shrinkage in addition to treadmilling d Transient assemblies compete for the available FtsZ pool d FtsZ protofilaments in the cytosol are less than 20 monomers long
MreB forms elongated structures that preferentially localize to areas of specific geometries. Deleting the MreB accessory factor RodZ reduces the number of structures and abolishes MreB's geometric localization. An unbiased machine learning analysis shows that the total length of MreB polymers, the number of MreB polymers and MreB curvature preference are key determinants of cylindrical uniformity, the variability in radius within a single cell. Changes in the values of these parameters are highly predictive of the resulting changes in cell shape (r 2 =0.93). Our data thus suggest RodZ promotes the assembly of geometrically-localized MreB polymers that lead to the growth of uniform cylinders. Shapes that are more complex than the straight rod have an added twist to their story and require additional protein determinants. We further study localization of the shape determining proteins in two human pathogens: comma-shaped Vibrio cholerae and helical-rod shaped Helicobacter pylori. V. cholerae localizes its shape determining protein CrvA along the inner, minor axis, while H. pylori localizes one of its shape determining proteins along the outer, major axis. Deleting these shape determinants results in greatly perturbed cell shapes and severe defects in colonizing animal hosts, underscoring the importance a bacterium's shape has to its successful lifestyle. 1601-Plat Dynamics of Bacterial Cell Wall Synthesis Proteins during CytokinesisXinxing Yang, Jie Xiao. Johns Hopkins Univ, Baltimore, MD, USA. In Gram-negative bacteria E. coli, cell division started from recruiting FtsZ to the mid-cell and form a highly dynamic but organized ring-like structure. FtsZ and its membrane tether proteins further recruit other components to complete a machinery which proceeds the cell division process. Our study has shown the FtsZ-ring is clustered and treadmills around the cell circumference 1 . Unlike FtsZ, FtsI (or PBP3) which is one of the cell wall synthesis proteins moves directionally around the septum. Its average velocity is highly correlated with the treadmilling speed of FtsZ filaments. How these proteins are directed by FtsZ and coordinated with the peptidoglycan network is still unclear. Here, we implemented single molecule tracking to monitor the dynamics of FtsI and another essential glycosyltransferase, FtsW in real time. We checked the population and velocity changes with FtsZ mutants and FtsI inhibitor treatment. Comparing the correlation of the mobility of those proteins with both FtsZ treadmilling and enzymatic activity led us to a model which explains how the cell wall synthesis system is coordinated with the cytoskeleton system. How cells regulate their growth rate in response to nutrient conditions remains an outstanding question in biology. Bacteria are surrounded by a peptidoglycan cell wall that holds their shape. This structure is built by MreB filaments that regulate the enzymes that synthesize the cell wall. Collectively termed the Rod Complex, these machines moving around the cell as they insert new materi...
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
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