Communication across the bacterial cell envelope depends on the size of the periplasm
Fig 2
Lpp dictates the distance between the IM and the OM in Escherichia coli.
(A) Cryo-EM revealed uniform membrane structures with WT cells, but lppΔK58 cells, in which Lpp can no longer bind peptidoglycan, displayed blebbing of the OM. E. coli strains expressing longer Lpp variants (lpp+14 and lpp+21) did not bleb or exhibit membrane defects, similar to WT (S5 Fig). (B) From cryo-EM projection images, distances between the IM and the OM were measured along the cell axis (while avoiding substantial blebbing regions in cells expressing LppΔK58) and plotted in 1-nm bins. The lppΔK58 mutant strain had a periplasmic (IM-to-OM) distance that was about 3 nm larger than that of the WT strain (P < 0.0001, Kruskal-Wallis) and had a much broader spread of data. The lpp+14 and lpp+21 mutant strains had periplasmic distances that were 3 nm and 4 nm, respectively, larger than WT (P < 0.0001, Kruskal-Wallis), indicating that the IM-to-OM distance varies as a function of the length of Lpp. Avg, average; cryo-EM, cryo-electron microscopy; IM, inner membrane; Lpp, Braun’s lipoprotein; OM, outer membrane; WT, wild-type.