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Sun, Yingjie

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Sun

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Yingjie

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Sun, Yingjie
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    Bacillus subtilis cell diameter is determined by the opposing actions of two distinct cell wall synthetic systems
    (Springer Science and Business Media LLC, 2019-05-13) Dion, Michael; Kapoor, Mrinal; Sun, Yingjie; Wilson, Sean; Ryan, Joel; Vigouroux, Antoine; van Teeffelen, Sven; Oldenbourg, Rudolf; Garner, Ethan
    Rod shaped bacteria grow by adding material into their cell wall via the action of two spatially distinct enzymatic systems: The Rod system moves around the cell circumference, while the class A penicillin-binding proteins (aPBPs) are unorganized. To understand how the combined action of these two systems defines bacterial dimensions, we examined how each system affects the growth and width of Bacillus subtilis, as well as the mechanical anisotropy and orientation of material within their sacculi. We find that rod diameter is not determined by MreB, rather it depends on the balance between the systems: The Rod system reduces diameter, while aPBPs increase it. RodA/PBP2A can both thin or widen cells, depending on its levels relative to MreBCD. Increased Rod system activity correlates with an increased density of directional MreB filaments, and a greater fraction of directionally moving PBP2A molecules. This increased circumferential synthesis increases the amount of oriented material within the sacculi, increasing their mechanical anisotropy and reinforcing rod shape. Together, these experiments explain how the combined action of the two main cell wall synthetic systems build rods of different widths, a model that appears generalizable: Escherichia coli containing Rod system mutants show the same relationship between the density of directionally moving MreB filaments and cell width.
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    MreB filaments align along greatest principal membrane curvature to orient cell wall synthesis
    (eLife Sciences Publications, Ltd, 2018) Hussain, Saman; Wivagg, Carl N; Szwedziak, Piotr; Wong, Felix; Schaefer, Kaitlin; Izoré, Thierry; Renner, Lars D; Holmes, Matthew; Sun, Yingjie; Bisson-Filho, Alexandre W; Walker, Suzanne; Amir, Ariel; Löwe, Jan; Garner, Ethan
    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.