Fig. 1: PapS has a decisive role in R. rubrum cell curvature.

a Total protein abundance in R. rubrum wild-type (S1) cells, as estimated on the basis of iBAQ (intensity-based absolute quantification) values derived from whole-cell proteome analysis. The graph on the left shows all 1943 proteins detected ranked according to their cellular abundance level. The red box indicates the 40 most abundant proteins, whose levels are further detailed in the graph on the right. Relevant proteins are highlighted in red. b β-lactam resistance assay confirming the periplasmic localization of PapS. Cells of strains S1 (WT), SP231 (papS-bla) and SP01 (papS-mCherry) were streaked on solid medium without or with ampicillin (200 µg ml^-1). Ampicillin resistance indicates the translocation of PapS-Bla to the periplasm. c Structural model of R. rubrum PapS, generated with AlphaFold2³⁸ and shown in the predicted cell envelope context (OM: outer membrane, PG: peptidoglycan). The N-terminal domain is shown in turquoise, the linker in grey and the OmpA-like peptidoglycan-binding domain in dark blue. The scheme at the bottom shows the position of the different domains in the amino acid sequence of PapS (SP: signal peptide, aa: amino acids). d Microscale thermophoresis analysis investigating the interaction of the OmpA-like peptidoglycan-binding domains (100 nM) of R. rubrum PapS and PapS_R223A (amino acids 156-273) and A. baumannii OmpA (amino acids 221-339) with increasing concentrations of mDAP. Data represent the mean (±SD) of 3 independent experiments. The resulting K_D values are indicated next to the respective binding curves. e Morphology of R. rubrum wild-type (S1) and ΔpapS (JR52) cells, visualized by phase-contrast microscopy. Bar: 5 µm. f Superplots showing the distribution of cell sinuosities in populations of R. rubrum wild-type (S1) and ΔpapS (JR52) cells and of ΔpapS cells expressing a complementing copy of papS from a low-copy number plasmid (compl.; JR54). Small dots represent the data obtained in three independent biological replicates (shown in dark blue, light blue and grey; n = 100 cells per replicate). Large dots represent the mean value of the three datasets. The red horizontal line indicates the average of these three mean values. The statistical significance (p value) of differences between the wild type and the two mutant strains is indicated (unpaired two-sided Welch’s t-test). g Purified peptidoglycan sacculi of R. rubrum wild-type (S1) and ΔpapS (JR52) cells, visualized by phase-contrast microscopy. Black dots likely represent polyhydroxybutyrate granules⁹². Bar: 5 µm. h Superplots showing the sinuosities of peptidoglycan sacculi isolated from R. rubrum wild-type (S1) and ΔpapS (JR52) cells. The data are presented as described in panel (f) (n = 100 cells per replicate). The statistical significance (p value) of differences between the wild type and the two mutant strains is indicated (unpaired two-sided Welch’s t-test). Source data are provided as a Source Data file.