MreB Filaments Create Rod Shape By Aligning Along Principal Membrane Curvature

Abstract

24MreB is essential for rod shape in many bacteria. Membrane-associated MreB filaments 25 move around the rod circumference, helping to insert cell wall in the radial direction to 26 reinforce rod shape. To understand how oriented MreB motion arises, we altered the 27 shape of Bacillus subtilis. MreB motion is isotropic in round cells, and orientation is 28 restored when rod shape is externally imposed. Stationary filaments orient within 29 protoplasts, and purified MreB tubulates liposomes in vitro, orienting within tubes. 30Together, this demonstrates MreB orients along the greatest principal membrane 31 curvature, a conclusion supported with biophysical modeling. We observed that 32 spherical cells regenerate into rods in a local, self-reinforcing manner: rapidly 33 propagating rods emerge from small bulges, exhibiting oriented MreB motion and 34 increased glycan crosslinking. We propose that the coupling of MreB filament alignment 35 to shape-reinforcing peptidoglycan synthesis creates a locally-acting, self-organizing 36 mechanism allowing the rapid establishment and stable maintenance of emergent rod 37 shape.

How to Build a Bacterial Cell: MreB as the Foreman of E. coli Construction

“…Different studies have used different metrics and sign conventions to quantify MreB’s curvature-based localization, making their absolute measurements difficult to compare directly. However, all analyses agree that MreB strongly avoids bulging regions like the poles and enriches locally where inward surface indentations occur, including at the necks of regions with cell bulges (Billings et al, 2014; Hussain et al, 2017; Ursell et al, 2014) (Figure 4). Furthermore, the existence of rod-shaped E. coli mutants that inhibit MreB’s rotational motion but retain MreB’s curvature-based localization preference indicates that curvature preference is not simply due to time-averaging of circumferential rotation (Morgenstein et al, 2015; Morgenstein et al, 2017).…”

“…Disruption of MreB assembly by A22 treatment caused more uniform growth across the cell surface, with wall insertion commencing at the poles (Ursell et al, 2014). Conceptually similar experiments following the process by which E. coli (Billings et al, 2014) or B. subtilis (Hussain et al, 2017) reform rods from spheres reinforced the conclusion that cells insert new cell wall material specifically at the sites where MreB localizes, even in amorphous or irregularly-shaped cells. Thus, MreB polymers spatially dictate the subcellular sites of growth.…”

“…Studies of intracellular organization and morphogenesis have been greatly facilitated by computational tools that enable automated, high-throughput quantification of cell shape and fluorescence from microscopy images (Ducret et al, 2016; Paintdakhi et al, 2016; Stylianidou et al, 2016; Ursell et al, 2017). These software packages have been able to achieve subpixel resolution of cell contours, enabling quantification of cellular dimensions (Campos et al, 2017; Hussain et al, 2017; Ursell et al, 2017), the degree of cell straightness and width variation (Morgenstein et al, 2015; Morgenstein et al, 2017; Ouzounov et al, 2016), and the correlation of protein localization with cell geometry (Renner et al, 2013; Ursell et al, 2017; Wong et al, 2017).…”

“…Furthermore, the existence of rod-shaped E. coli mutants that inhibit MreB’s rotational motion but retain MreB’s curvature-based localization preference indicates that curvature preference is not simply due to time-averaging of circumferential rotation (Morgenstein et al, 2015; Morgenstein et al, 2017). Curvature-based localization may be a generally conserved property of MreB, as B. subtilis MreB is also recruited to the necks of cell bulges (Hussain et al, 2017) and purified Thermatoga maritima MreB polymers curve membranes in vitro (Salje et al, 2011).…”

Evolutionary rescue of sphericalmreBdeletion mutants of the rod-shape bacteriumPseudomonas fluorescensSBW25

“…MreB filaments participate in establishing the width and stiffness of the cell while 59 exerting an inward force on the cell wall [26][27][28][29][30] . MreB is also known to have other 60 pleitotropic effects on a range of cellular functions and its loss is frequently lethal in 61 model microbial systems 12 .…”