Cell-wall synthases contribute to bacterial cell-envelope integrity by 2 actively repairing defects 3
Abstract
Cell shape and cell-envelope integrity of bacteria are determined by the peptidoglycan 12 cell wall. In rod-shaped Escherichia coli, two conserved sets of machinery are essential for cell-wall 13 insertion in the cylindrical part of the cell, the Rod complex and the class-A penicillin-binding 14 proteins (aPBPs). While the Rod complex governs rod-like cell shape, aPBP function is less well 15 understood. aPBPs were previously hypothesized to either work in concert with the Rod complex 16 or to independently repair cell-wall defects. First, we demonstrate through modulation of enzyme 17 levels that class-A PBPs do not contribute to rod-like cell shape but are required for mechanical 18 stability, supporting their independent activity. By combining measurements of cell-wall stiffness, 19 cell-wall insertion, and PBP1b motion at the single-molecule level we then demonstrate that PBP1b, 20 the major class-A PBP, contributes to cell-wall integrity by localizing and inserting peptidoglycan in 21 direct response to local cell-wall defects. 22 23
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