An outer membrane porin-lipoprotein complex modulates elongasome movement to establish cell curvature in Rhodospirillum rubrum

Curved cell shapes are widespread among bacteria and important for cellular motility, virulence and fit-ness. However, the underlying morphogenetic mechanisms are still incompletely understood. Here, we identify an outer-membrane protein complex that promotes cell curvature in the pho¬tosynthetic species Rhodo¬spirillum rubrum. We show that the R. rubrum porins Por39 and Por41 form helical ribbon-like struc-tures at the outer curve of the cell that recruit the peptido¬glycan-binding lipo¬pro¬tein PapS, with PapS in-activation, porin de¬localization or disruption of the porin-PapS interface resulting in cell straight¬ening. We further demonstrate that porin-PapS assemblies act as molecular cages that entrap the cell elon¬gation ma-chine¬ry, thus biasing cell growth towards the outer curve. These findings reveal a mechanistically dis¬tinct mor¬pho¬genetic module medi¬ating bacterial cell shape. Moreover, they uncover an unprecedented role of outer-mem¬brane pro¬tein pat¬terning in the spatial control of intracellular processes, adding an important facet to the reper¬toire of regu¬la¬tory mechanisms in bac¬terial cell biology.