Fig. 4: Cell wall composition affects the integrity and organization of the outer membrane.

a, Co-labelling of PG and the OMP FepA in a pentapeptide-rich strain (CS703-1). PG labelling (HADA) and FepA induction (0.4% arabinose) were initiated simultaneously for a total period of 7 min. Arrows indicate cells showing disparity between OMP and PG biogenesis. b, The fluorescence intensity of FepA versus HADA in tetrapeptide-rich (left) and pentapeptide-rich (right) strains following co-labelling as in a. The representative pixel-by-pixel cytofluorograms of single images show that the strong correlation of OMP and PG biogenesis is abrogated in the pentapeptide-rich strain. c, Polar displacement assay whereby mid-cell OMP biogenesis bias can be discerned from the movement of stationary phase FepA as cells revive. Representative images before and after resuspension in fresh medium (top) and an illustration of OMP movement during this period (bottom). d, Polar displacement of stationary phase FepA during revival. Representative images (top) and demographs of normalized fluorescence intensities across multiple cells (bottom) 45 min after resuspension in fresh M9 medium. The images and demographs show how differently OMPs segregate between tetrapeptide-rich and pentapeptide-rich strains. e, Effect of PG remodelling by plasmid-produced PBP5 on SDS sensitivity in CS703-1 and CS703-1Δlpp. Ectopic PBP5 production from pdacA partially restores outer membrane integrity. f, Model for spatial coupling of PG biosynthesis and BAM activity in the cell. BAM-mediated OMP insertion is dampened by mature PG, resulting in OMP biogenesis being largely absent at the old poles of cells and occurring predominantly at PG growth sites.