MreB is essential for rod shape in many bacteria. Membrane-associated MreB filaments move around the rod circumference, helping to insert cell wall in the radial direction to reinforce rod shape. To understand how oriented MreB motion arises, we altered the shape of Bacillus subtilis. MreB motion is isotropic in round cells, and orientation is restored when rod shape is externally imposed. Stationary filaments orient within protoplasts, and purified MreB tubulates liposomes in vitro, orienting within tubes. Together, this demonstrates MreB orients along the greatest principal membrane curvature, a conclusion supported with biophysical modeling. We observed that spherical cells regenerate into rods in a local, self-reinforcing manner: rapidly propagating rods emerge from small bulges, exhibiting oriented MreB motion. We propose that the coupling of MreB filament alignment to shape-reinforcing peptidoglycan synthesis creates a locally-acting, self-organizing mechanism allowing the rapid establishment and stable maintenance of emergent rod shape.

How proteins in the bacterial cell division complex (the divisome) coordinate to divide bacteria remains unknown. To explore how these proteins collectively function, we conducted a complete dynamic characterization of the proteins involved, and then examined the function of FtsZ binding proteins (ZBPs) and their role in cytokinesis. We find that the divisome consists of two dynamically distinct subcomplexes: stationary ZBPs that transiently bind to treadmilling FtsZ filaments, and a directionally-moving complex that includes cell wall synthases. FtsZ filaments treadmill at steady state and the ZBPs have no effect on filament dynamics. Rather, ZBPs bundle FtsZ filaments, condensing them into Z rings. Z ring condensation increases the recruitment of cell wall synthesis enzymes to the division site, and this condensation is necessary for cytokinesis. Main Text:The mechanism by which bacteria divide remains poorly understood. In most bacteria, division begins when filaments of FtsZ, a tubulin homolog, form a "Z ring" at midcell (1). The Z ring then recruits other cell division proteins, collectively called the divisome (Fig 1A). The first group of these proteins (early proteins) arrives concurrently with FtsZ and includes the actin homolog FtsA and several other FtsZ binding proteins (ZBPs): EzrA, SepF, and ZapA. The second group of integral membrane proteins (late proteins) is then recruited, including DivIB, DivIC, and FtsL, and the cell wall synthesis enzymes Pbp2B and FtsW (2, 3). During cytokinesis, the Z ring constricts while the associated cell wall synthesis enzymes build a septum that divides the cell in half (4). Recent work has shown that FtsZ filaments treadmill around the division plane, moving at the same rate as the transpeptidase Pbp2B. (5, 6) (Movie S1). FtsZ treadmilling dynamics are critical for cell division: In Bacillus subtilis, the rate of treadmilling limits Pbp2B motion, the rate of septal cell wall synthesis, and the overall rate of septation (5).To understand how these proteins work to divide cells, we sought to build a dynamic characterization of how this multi-component machine functions in B. subtilis. We first worked to identify groups of divisome proteins that move together, then investigated how the FtsZ-.

AbstractHow proteins in the bacterial cell division complex (the divisome) coordinate to divide bacteria remains unknown. To explore how these proteins collectively function, we conducted a complete dynamic characterization of the proteins involved, and then examined the function of FtsZ binding proteins (ZBPs) and their role in cytokinesis. We find that the divisome consists of two dynamically distinct subcomplexes: stationary ZBPs that transiently bind to treadmilling FtsZ filaments, and a directionally-moving complex that includes cell wall synthases. FtsZ filaments treadmill at steady state and the ZBPs have no effect on filament dynamics. Rather, ZBPs bundle FtsZ filaments, condensing them into Z rings. Z ring condensation increases the recruitment of cell wall synthesis enzymes to the division site, and this condensation is necessary for cytokinesis.

In Bacillus subtilis the deoxyribonucleic acid content and the extent of cell division during inhibition of chromosome replication increased as a function of the average cell mass, independent of the growth rate. At each growth rate, mass, deoxyribonucleic acid, and residual division varied in different cultures. The variation is consistent with a large variability in the D period. At growth rates higher than 1.5 doublings per h at 37 degrees C, the change in D accounts for the growth rate dependence of the mass and deoxyribonucleic acid content.

MreB is essential for rod shape in many bacteria. Membrane-associated MreB filaments move around the rod circumference, helping to insert cell wall in the radial direction to reinforce rod shape. To understand how oriented MreB motion arises, we altered the shape of Bacillus subtilis. MreB motion is isotropic in round cells, and orientation is restored when rod shape is externally imposed. Stationary filaments orient within protoplasts, and purified MreB tubulates liposomes in vitro, orienting within tubes. Together, this demonstrates MreB orients along the greatest principal membrane curvature, a conclusion supported with biophysical modeling. We observed that spherical cells regenerate into rods in a local, self-reinforcing manner: rapidly propagating rods emerge from small bulges, exhibiting oriented MreB motion. We propose that the coupling of MreB filament alignment to shape-reinforcing peptidoglycan synthesis creates a locally-acting, self-organizing mechanism allowing the rapid establishment and stable maintenance of emergent rod shape.